project on advanced monitoring system for gis substation

CHAPTER 1

INTRODUCTION

1.1 OBJECTIVE OF PROJECT

        G.I.S substations are preferred in cosmopolitan cities, industrial townships etc where cost of land is very high and cost of G.I.S is justified by saving due to reduction in floor area requirements. In these substations, sulphur hexafluoride (SF6) gas is used in switchgear as insulating and arc quenching media. Various components like circuit breakers, busbars, disconnectors, current transformers, voltage transformers, earthing switches etc. are housed in metal modules filled with SF6 gas.

     As the dielectric strength of SF6 gas is higher than air, the overall size of each equipment and the complete substation is reduced to about 10% of conventional air insulated substations. When a typical 220KV substation of 5 breaker ring bus arrangement occupies an overall area of 100m*40m, the GIS for the same arrangement will require only 24m*9m area. To reduction in site are will be by 19/20 of the conventional substation. Volume wise it is only 1/60 of the conventional substations. The various modules are factory assembled are filled with SF6 gas. Such substations are compact and can be installed conveniently on any floor of a multistoried building or in underground substations. All the main elements of the substation area are completely enclosed in SF6 installation, which include circuit breakers, loadbreak switches, isolators, earth switches, current transformers, potential transformers, busbars, coupling capacitors and SF6 lead out bushing insulators for connection to overhead lines, transformers or other external equipments. Equipments such as transformers, shunt reactors, shunt capacitors, carrier communication, line traps etc. are not part of the SF6 insulated system.

      During the last 35 years many GIS have been installed and successfully operated worldwide. In India the first G.I.S was installed in Mumbai more than 15 years ago and now a large numbers of units are either in operation or in the process of being commissioned. Now G.I.S substations are available from voltage ranges, 72.5KV to 1100KV in all types of busbar arrangements. In Kerala, at Thiruvanthapuram two GIS substations are installed and are under working conditions at Power house and LA complex.

       From the load study conducted in Kollam city, we can see that, the present load is 43MVA and the load rises by about 6% annually. Moreover the number of power interruptions can be reduced to a great extent if we set up a G.I.S substation in Kollam city. With the existing system voltage drop is also very high which can be minimized if the proposed system is set up. Unlike a conventional substation which needs acres of land; and that too in the heart part of the city which is almost impossible in the current situation, a G.I.S substation which occupies only 10% space compared to a conventional substation is adequate. Hence the objective is to design a 110KV substation in the powerhouse compound of Kollam city with an advanced control room.

      Kollam city is a Municipal Corporation in Kollam district in the Indian state of Kerala. It lies 71 Km north of the state capital Thiruvanathapuram. It is also the headquarters of the Kollam District, one among the 14 districts in the state of Kerala. It is bound on south by Thiruvanathapuram district, on the north by Pathanamthitta and Alappuzha, on the east by Tamil Nadu and on the west by the Arabian Sea. The town is very famous for cashew processing and coir manufacturing. It is the southern gateway to the backwaters of Kerala, and thus, a prominent tourist destination.

       The geographical coordinates for Kollam are 9.28’45° N 76.28’0° E. The district covers an area of 2,492 km² and ranks seventh in the State with respect to area. Kollam like other districts in the state is moderately industrialized. Some of the major employers in the public sector are Indian Rare Earth (IRE), Kerala Metals and Minerals Limited at Chavara; United Electrical Industries (popularly known as the Meter Company) and Parvathi Spinning Mills at Kollam. Cashew processing and coir production are the two most important sources of employment.

 MAP OF KOLLAM CITY

1.2 SWITCH GEAR COMPONENTS OF A SUBSTATION

      During the operation of the power system the generating plants, transmission lines, distributors and other electrical equipments are required to be switched on or off under both normal and abnormal operating conditions. The apparatus including its associated auxiliaries employed for controlling, regulating or switching on or off the electrical circuits in the electrical power system is known as switch gear.

      With the advancement of electrical power systems, the lines and other equipment operate at very high voltage and carry large current. Whenever a short-circuit occurs, a heavy current flows through the equipment causing considerable damage to the equipment and interruption of service, so in order to protect the lines, generators, transformers and other electrical equipment from damage automatic protective device or switchgear is required.

1.2.1 SWITCHES

      A switch is used in an electric circuit as a device for making or breaking the electric circuit in a convenient way i.e. by the simple motion of a knob or handle to connect together or disconnect two terminals to which wires or cables are connected. The switches may be classified into

a)      Air switches

    i)Air-break switches

    ii)Oil switches

b)      Oil switch

      As their names imply, air switches are those whose contacts are opened in air, while oil switches are those whose contacts are opened under oil. Oil switches are usually employed in very high voltage heavy current circuits. Air switches are further classified as air-break switches and isolators (or disconnector switches).

i) AIR-BREAK SWITCHES:

      The air break switch has both the blade and the contact equipped with arcing horns. Arcing horns are piece of metal between which the arc resulting from opening a circuit carrying current is allowed to form. As the switch opens, these horns are spread father apart and the arc is lengthened until it finally breaks.

      Air-break switches are of several designs. Some are operated from the ground by a hook on the end of a long insulated stick: some others through a system of linkage are opened by a crank at the foot of the pole. Where more than one conductor is opened, there may be several switches mounted on the same pole. These may be opened singly or altogether in a “gang” as this system is called. Some switches are mounted so that the blade opens download and these may be provided with latches to keep the knife blade from jarring open.

ii)ISOLATORS:

      Isolators (or disconnect switches) are not equipped with arc quenching device and therefore not used to open circuits carrying current. As the isolator isolates one portion of the circuit from another and is not intended to be opened while current is flowing. Isolators must be opened until the circuit is interrupted be some other means. If an isolator is opened carelessly, when carrying a heavy current, the resulting arc could easily cause a flash over to earth. This may shatter the supporting insulators and may even cause a fatal accident to the operator, particularly in high voltage circuits. While closing a circuit, the isolators is closed first, then circuit breaker. Isolators are necessary on supply side of circuit breakers in order to ensure isolation (disconnection) of the circuit breaker from the lie parts for the purpose of maintenance.

1.2.2 PROTECTIVE EQUIPMENT

      Protective equipment is an extremely important item in system design it is installed to  function under abnormal conditions to prevent failure or isolate trouble and limit its effect. It must function reliably and quickly. It should be selected for greatest reliability, speed of operation, and simplicity and should be consistent with the system design.

1.2.2.1 CIRCUIT BREAKERS

       A circuit breaker is a mechanical device designed to close or open contact members, thus closing or opening an electrical circuit under normal or abnormal conditions. It is so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault conditions. An automatic circuit breaker is equipped with a trip coil connected to a relay or other means, designed to open or break is closed, considerable energy is stored in the springs. The contacts are held together by means of toggles. To open the circuit breaker, only a small pressure is required to be applied on a trigger. When the trigger is actuated by the protective relay, it trips and the potential energy of the springs is released and the contacts open in a fraction of seconds.

       A circuit breaker must carry normal load currents without over heating or damage and must quickly open short-circuit currents without serious damage to itself and with a minimum burning of contacts. Circuit breakers are rated in maximum voltage, maximum continuous current carrying capacity, maximum interrupting capacity and maximum momentary and 4 second current carrying capacity.

       The breakers are provided with operating mechanisms which are in turn, actuated by power supplied through suitable relays. In indoor substations, breakers of high rupturing capacities are enclosed in fire-proof compartments. Lift-up or draw out type breakers which incorporate a disconnect feature on each side are the most common in design and applications. Air circuit breakers are often employed instead upto 15KV in these units and oil recloser is sometimes employed to cut down the cost in small rural substations.

Thus the functions of a circuit breaker are

·         To carry full-load current continuously.

·         To open and close the circuit on load.

·         To make and break the normal operating current.

·         To make and break the short-circuit current of magnitude upto which it is designed for.

1.2.2.2 PROTECTIVE RELAYS

       The protective relay is an electrical device interposed between the main circuit and the circuit breaker in such a manner that any abnormality in the circuit acts on the relay, which in turn, if the abnormality is if a dangerous character, causes the breaker to open and so it isolate the faulty element. The protective relay ensure the safety of the circuit equipment from any damages which might otherwise caused by the fault.

1.      Sensing element, sometimes also called the measuring elements, responds to the change in the actuating quantity, the current in a protected system in case of over-current relay.

2.      Comparing element sieves to compare the action of the actuating quantity on the relay with a pre-selected relay setting.

3.      Control element on a pick of the relay, accomplishes a sudden change in the control quantity such as closing of the operative current circuit.

1.2.2.3 CURRENT TRANSFORMERS (CT’s)

      These instrument transformers are connected in newer circuits to feed the current coils of indicating and metering instrument (ammeter, wattmeter and watt-hour meters) and protective relays. Thus the CT’s broaden the limits of measurements and maintain a watch over the currents flowing in the circuit and over the power loads. In high voltage installations CT’s in addition to above also isolate the metering instruments from high voltage.

      The current transformers basically consist of an iron-core on which are wound a primary and one or two secondary windings. The primary is directly inserted in the power circuit (the circuit in which current is to be measured) and to the secondary winding or windings the indicating and metering instruments and relays are connected. When the rated current of CT flows through its primary winding a current of 5 ampere will appear in its secondary winding. The primary winding is usually single turn winding and the number of turns on secondary winding depends upon the power circuit current to be measured. The larger current to be measured more the numbers of turns on secondary. The ratio of primary current to the secondary current is known as transformation ratio of CT.

      The current transformers are rated for rated voltage of the installation, the rated currents of the primary and secondary windings and the accuracy class. The accuracy class indicates the limit of the error in percentage of the rated turns ratio of the given current transformer. Current transformers are available in the accuracy classes 0.5, 1, 3 and 10.

1.2.2.4 POTENTIAL TRANSFORMERS (PT’s)

       The potential transformers are employed for voltages above 380 volts to feed the potential coils of indicating and metering instruments (voltmeters, wattmeters, watt-hour meters) and relays. The transformers make the ordinary low voltage instruments suitable for measurement of high voltage and isolate them from high voltage. The primary winding of the potential transformer is connected to the main bus-bars of the switchgear installation and to the secondary winding, various indicating and metering instruments and relays are connected.

     When the rated high voltage is applied to the primary of a PT, the voltage of 110volts appears across the secondary winding. The ratio of the rated primary voltage to the rated secondary voltage is known as turns transformation ratio. The potential transformers are rated secondary are rated for primary and secondary rated voltage accuracy class, number of phases and system of cooling.

1.2.2.5 LIGHTNING ARRESTERS

       The lightning arrester is a surge diverter and is used for the protection of power system against the high voltage surges. It is connected between the line and earth and so diverts the incoming high voltage wave to the earth. Lightning arresters act as safely valves designed to discharge electric surge resulting from lightning strokes, switching or other disturbances, which would otherwise flashover insulators or puncture insulation, resulting in a line outage and possible failure of equipment. They are designed to absorb enough transient energy to prevent dangerous reflections and to cut off the flow of power frequency follow (or dynamic) current at the first current zero after the discharge of the transient. They include one or more sets of gaps to establish the breakdown voltage, aid in interrupting the power follow current, and prevent any flow of current under normal conditions (except that step shunting resistors, when used to assure equal distribution of voltage across the gaps permits a very small leakage current). Either resistance (valve) elements to limit the power follow current to values the gaps can interrupt, or an additional arc extinguishing chamber to interrupt the power follow current are connected in series with gaps. Arresters have a short time lag of breakdown compared with the insulation of apparatus the breakdown voltage being nearly independent of the steepness of the wave front.

       Transmission line is protected from direct strokes by running a conductor known as ground wire, over the towers or poles and earthed at regular intervals preferably at every pole/tower.

      Substations, interconnectors and power houses are protected from direct strokes by earthing screen that consists of a network of copper conductors, earthed atleast on two points, overall the electrical equipment in the substation. The ground wire or earthing screen does not provide protection against the high voltage waves reaching the terminal equipment, so some protective devices are necessary to provide protection to power stations, substations and transmission lines against the voltage wave reaching there. The most common device used for the protection of the power system against the high voltage surge is surge diverter which is connected between line and earth and so diverts the incoming high voltage wave to earth. Such a diverter is also called the lighting arrester.

        Different types of gaps and lightning arresters (rod gap, horn gap, electrolytic arrester, oxide film arrester, thyrite arrester, expulsion type lightning arrester, valve type lightning arrester) etc.

1.2.2.6 EARTHING OF POWER SYSTEM

     The term ‘earthing’ means connecting of non-current carrying part of the electrical equipment or the neutral point of the supply system to the general mass of earth in such a manner that at all times an immediate discharge of electrical energy takes place without danger.  The earthing is provided with the following objective.

·         For the safety of equipment and personnel lighting and voltage surges providing the discharge path for lightning arresters, gaps and similar devices.

·         For providing ground connections for ground neutral systems.

·         For providing a means of positively discharging and de-energizing feeders or equipment before proceeding with maintenance on them.

·         For safety of personnel from the electric shock ensuring that non-current carrying parts, such as equipment frames are always safely at ground potential even though insulation fails.

       Grounding of power systems is highly important. A substantial and adequate ground that will not burn off or permit dangerous rise in voltage under abnormal conditions is essential. Extensive damage and dangerous conditions have arisen when inadequate grounds have been provided. Multiple ground and multiple connections to them are usually desirable to ensure ground protections, even though one ground or connection opens owing to burn-off or other conditions such as high resistance. The station earthing system should have low resistance. The station earthing system should have low resistance.

      The earthing can be divided into neutral and equipment earthing .Neutral earthing (or grounding) deals with the earthing of the system neutral to ensure system security and protection. Neutral earthing is also called the system earthing. Equipment earthing or safety earthing deals with earthing of non- current carrying parts  of the equipment ensures safety of potential and protection against lightning. Equipment earthing also helps in earth fault protection. The earthed parts remain at approximately earth potential even during flow of fault current.

     In neutral earthing, the points (star point) of star connected 3-phase winding of power transformers, generators, motors, earthing transformers are connected to low resistance ground. The chief advantage s of neutral earthing are:

·         Persistence arching ground can be eliminated by employing suitable protective gear.

·         Earth fault can be utilized to operate protective relays to isolate the fault.

·         The voltage of healthy phases remains nearly constant.

·         Induced static charges are conducted to earth without disturbance.

·         There is a possibility of installing discriminative protective gears on such systems.

·         This system gives reliable service and greater safety to personnel’s and equipment.

·         Maintenance and operating cost of such systems over isolated system is comparably less.

1.2.2.7 CONTROL ROOMS

     The control room (or the remaining room) is the nerve center of a power station. The various controls preferred from here are voltage adjustment load control, emergency tripping of turbines etc. and the equipment and instruments housed in a control room are synchronizing equipment isolators, relays, ammeter and watt meters, KWh meters.

      The location of control room in relation to other sections of the power station is also very important. It should be located away from the source of noise and should be near the switch house so as to save multi-core cables used for interconnection of course, if there is any fire in switch house, the control room should remain unaffected. Also here should be access from the control room to the turbine house. The control room should be neat and clean, well-ventilated, well lighted and free from droughts. There should be no glare and the colour scheme should be soothing to eyes. The instrument should have scales clearly marked and properly calibrated and all the apparatus and circuit should be labeled so that they are clearly visible.

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CHAPTER 2

STUDY OF GIS SUBSTATION

2.1INTRODUCTION

Substations where gas is used in the switchgear as switching medium, insulating medium and as arc quenching medium are called G.I.S. substation. SF6 gas is used for this purpose due to its chemical and thermal characteristics.

2.2MAIN FEATURES

·         Single phase enclosed design.

·         Small dimensions allowing economical space saving.

·         Indoor and outdoor applications.

·         High reliability in service, independent of ambient influences.

·         Flexibility and optimal arrangement of equipment, assured by highly modular element system.

·         Light weight, gas tight aluminum enclosures with low electrical losses and corrosion resistance.

·         Earthed enclosures assuring maximal protection against electrical shock for the operating personnel.

·         Low maintenance and long service life.

·         Environmental friendly behavior.

·         Epoxy resin barrier and support insulators.

·         Circuit breaker on single pressure principle actuated by hydraulic drive.

·         Protection against dangerous overpressure through bursting membranes.

·         Quick site assembly assured by infactory preassembled bays shipping units.

·         Compliance with international standards-IEC 517. IEC 694 etc.

2.3ADVANTAGES OF G.I.S OVER CONVENTIONAL TYPE

1.      Lesser Area

For conventional type of substations the yard equipment itself occupies a comparatively larger area say 40×40m approximately. This is in addition to the area required for the construction of the control room. It is estimated that the area required for the construction of 66KV substation including the control room is about 3.5 acres. But the area required for G.I.S substation is only less than 1/10^th of this, i.e. approximately 30 cents, as the equipments are enclosed in a metallic chamber and installed in control room itself.

      In bigger cities where space constraints pose a great problem the preference of G.I.S substation to conventional substations is justified.

2.      Easy Maintenance

     The fully metal enclosed principle adopted for the switchgears guarantees that no outside influence can, affect the insulating materials used in the assembly. Periodic maintenance such as cleaning the insulator, protection against corrosion etc, nominally applicable to conventional yard equipments are not necessary in G.I.S substations. Maintenance activities such as greasing, checking the driving mechanism of circuit breaker contacts, SF6 gas monitoring etc are very easy.

3.      Remote and Supervisory Control Facility

     Even though remote and supervisory control facility can be provided equally for air insulated substations also, the functioning of the various equipments are not fool proof. In the, since the operation will be trouble free.

4.      Future Expansion

     The expansion of G.I.S substation can be done within a short period compared with other types, if the expansion is foreseen at the time of construction by adding more additional bays

5.      Phenomena of Corona Discharge

     The corona discharge is a regular phenomenon for voltages above 110KV for outdoor construction. In a thickly populated area, this is quiet undesirable.

6.      General

      Since no structure is visible outside and even the transformers are kept  indoors. GIS substations will only add to the aesthetic beauty of the area.

     Salinity poses a serious threat especially to those substations which have proximity to the sea. Equipment structures get corroded due to salinity. This problem does not arise in the case of GIS substations as the yard equipments are enclosed. GIS station does not cause any pollution problem and even the humming of transformers is not audible outside, as the transformers are kept indoors.

2.4 SF6  GAS THEORY 

      SF6 gas is used in G.I switchgear as an insulating medium and as a switching gas due to its dielectric and arc quenching properties. The gas is produced by direct reaction at 300 degree centigrade between molten sulphur and fluorine gas, generated by electrolysis of hydrofluoric acid HF. It is chemically stable, non- toxic and incompressible. If SF6 is used at pressures which ensures that no liquefaction occurs, the problem with consideration droplets etc are also avoided.

2.4.1 SF6 AS AN INSULATING MEDIUM

Insulation by SF6 gas reduces the insulating distance i.e., the distance between the phases and two adjacent bays, thereby reducing the space required for a substation.

The gas is electronegative in character, that is, an atom or molecule of SF6 will attract and hold the electrons. The electronegative gases are good dielectrics.

From the graph above, the following observations can be made. Electric strength at 20 degree centigrade

SF6

1 bar 20 degree centigrade              -                75KV/cm

6bar 20 degrees centigrade             -                 375Kv/cm

AIR

1 bar 20 degree centigrade              -                30KV/cm

6 bar 20 degree centigrade              -                150Kv/cm

The above figures show that the withstand voltage of SF6 is 2.5 times higher than that of air under the same temperature and pressure. In other words, to meet the same voltage requirements SF6 requires an enclosure of lesser volume and weight than that required for air.

 In the case of internal fault the arc developed in SF6 has lower arc voltage than the arc in compressed air. This results in lower pressure increase in SF6 than in compressed air. The G.I switch gear is so designed that this pressure increase can be accommodated in the circuit breaker with less difficulty. Due to large density of sf6 the thermal conductivity is also high, the ratio for the same SF6/air is 2.5:1. Hence the dissipation of the generated heat by the ohmic resistance of the conductors via. The enclosure is more in case if SF6 than that of air. But is rather expensive and hence its leakage percentage has to reduced has to reduced to minimum. A standard allowance for this is 1% per annum.

2.4.2 SF6 AS A SWITCHING GAS

    SF6 is also used as arc-extinguishing medium in circuit breakers of the G.I.S. Circuit breaker is the most important safety element in a power supply system. The C.B must be capable of interrupting large currents at high electro motive force.

    The only element that can change quickly from conductive to non-conductive condition is the electric arc. The C.B interrupts the current by the cooling of the electric arc .developed between the contacts after they have been opened. When the current wave passes through zero, the energy supplied to the arc equals zero and if there is sufficient cooling, current will be interrupted. After current interruption the transient recovery voltage will be applied to the gas column which is still hot. If the arc quenching medium has not regained its electric strength at this time, there is a possibility restriking of the arc.

    In SF6 circuit breaker, during the arcing period, SF6 gas is blown axially alone the arc. The gas removes the heat and reduces arc diameter during the decreasing mode of the current wave. The diameter becomes small during current zero and the arc is extinguished. Due to excellent property of SF6 gas maximum values it regains its dielectric properties after the final current zero and prevent the arc from restriking. The arc-time constant, which is the time required for a medium to regain its dielectric strength after final current zero, for SF6 as is of the order of a few micro seconds.

When switching to a short-line fault, the rate of rise of recovery voltage is so large that it is almost impossible to quench the arc with compressed air, and is difficult with oil. But with SF6 this is very simple due to its large arc-quenching capacity.

 In addition, SF6 has a good thermal conductivity in the temperature range of 2000-3000 degree Kelvin. Due to this high thermal conductivity, heat exchange between the hot ionized core and surrounding medium is very fast, which assists in excellent arc quenching.

2.4.3 GAS QUALITY

     The gas applied in switchgear should be clean without any pollutants. If the gas becomes heavily polluted through internal fault it should not be used any longer and refilling should be carried out. The gas for filling or replenishing is called the clean gas in operation is called operating gas.

2.5 ARRANGEMENT OF THE INSTALLATION

      In a G.I.S substation the EHT side is protected by gas insulated switchgear filled with SF6 gas. Switchgear suitable for operation up to 525KV has been developed, this switchgear features a compact and convenient layout, safety precaution for service personnel and high operational reliability. In general switchgear provides perfect system security under specified operating conditions. The switchgear is made up of different compartments in which all operating units in a three phase construction are contained. The compartments are-

1)      Circuit breaker compartment

2)      Bus bar compartment and

3)      Cable termination compartment  

These compartments are interconnected by means of disconnectors.

2.5.1 CIRCUIT BREAKER COMPARTMENT

      This compartment consists of a three phase conductor system. The fixed contact of the disconnections is mounted on this conductor system. From the conductor system conductive connection go via laminated contacts to the moving contacts of the three circuit breaker elements. From the holders of the fixed contact, the conductors for each phase are connected to a three phase conductor system. This connection is done via a current transformer. On this are located the knife shaped fixed contacts from the disconnected to the cable termination compartment. But in the case of a coupling panel, connection to this cable termination compartment is not applicable since these contacts apply to the disconnected of the second bus bar system. The circuit breaker in this condition is situated between the two bus bar disconnections. The three singe phase circuit breaker interrupters are driven by a hydraulic system mounted on the front of circuit breaker compartment.

      A cylindrical insulator is situated in the cable termination compartment. The knife shaped fixed contact from the disconnector are mounted on it. A three phase earthing switch is mounted on the upper wall of the cable termination compartment. Current transformer as are places per phase in the circuit breaker compartment between the circuit breaker and the cable or the transformer disconnector.

2.5.1.1 INTERRUPTER

     Interrupter is the active component in  the circuit breaker. An insulation cylinder is spitted between the flinch and the contact holder inside the contact holder a fixed piston is mounted on a tube with flow orifice. The laminated sliding contacts ensure that the current is conducted form the connection to the bus bar system via the contact holder housing to the copper shaft and the nominal and arcing contacts which are connected to it. The fixed part of the nominal and the arcing contacts are mounted in the second contact holder in which filler with molecular sieve is also located. The second contact holder is connected with the first by means of an insulation cylinder.

2.5.1.2 INTERRUPTER FUNCTIONING

Opening:

      During the opening of the interrupter the gas is being compressed between the piston and movable cylinder. After the opening of the nominal current contacts and the arcing contacts, arcing will occur over the latter. This arc heats the gas locally to some thousands of Kelvins. As long as arcing continues, the accompanying pressure increase will prevent the compressed gas in the cylinder from escaping. At the moment of the first occurrence of current zero the arc is extinguished and the gas escapes from the cylinder via gaps in the nozzle. The quality of the gas is so quickly restored by the flow of cool and clear SF6 gas that re-ignition will not take place and the recovery voltage us retained. The polluted gas is filtered in the filter which holds the pollutants.

Closing:

       During the closing operation of the interrupter the sequence is reversed, in order to allow filling of the compressor chamber with SF6, inlet valves are mounted in the non moving piston.

2.5.1.3 DRIVING MECHANISM OF THE CIRCUIT BREAKER

        The energy for opening and closing the interrupter is provided by the driving mechanism which consists of the mechanical part and hydraulic part. Hydraulic pump unit pressurizes and maintains the pressure in hydraulic system including the accumulator. This pump is driven by an electric motor. A hand pump is mounted in parallel for operating the circuit breaker during servicing and maintenance. Supply to the electric pump motor is 415/220V ac. When the pump units motor is activated, the oil is sucked from the tank and compressed via non-return to the accumulator. If the pressure of the hydraulic system goes beyond 300 bar the hydraulic safety valve mounted in the pump unit opens and safe pressure is maintained.

        The accumulator of a pressure cylinder with two chambers separated from each other by a floating piston. One chamber is filled with high pressure nitrogen and the other chamber which is connected to the hydraulic system is filled with oil while the hydraulic system is being pressurized, the piston is driven by the oil compressing the gas in the other chamber. During a switching on and off cycle the oil is driven at a great spread by the compressed gas in to the drive cylinder. The compressed gas thus as a spring. The oil volume in the accumulator is sufficient for the completion of an open-close-open cycle or to close-open cycles. The linear motion of the drive cylinder is converted in to a linear motion of the interrupter contacts by the mechanical part of the drive which consists of a number of levers shafts, driving rods etc. shaft goes through a gas tight sealing in the compartment and is connected by means of a crank to a system of 3 rods called tumblers. These tumblers convert the rotating motion of main shaft into linear motion of three driving rods and interrupter contacts.

 

                                   

 2.5.2 TERMINATION COMPARTMENT

    The circuit breaker is connected to high voltage termination compartment.  This termination compartment is made with:

Cables (dry, oil filled or gas pressure type)

Direct connections to a transformer

Bus trucking with SF6-Air bushing.

     For high voltages DC testing this compartment is provided with a facility that allows access to HV conductors without evacuating the compartment or even without lowering the pressure of the gas. This device allows test to be performed on the cable (HVDC, impulse) for cable fault detection without necessitating the opening of the compartment or the removal of the SF6 gas. For measuring and protection a voltage compartment can be housed on the termination compartment.

  2.5.3 BUS- BAR COMPARTMENT

      The Bus bar system is mounted on the top of the circuit breaker compartment. This is constructed from sections with the same length as the normal panel width. The ends of the compartments are sealed off by means of raised covers. Three phase conductor system is suspended from trident insulators.  The disconnections knife shaped fixed contacts are situated on the conductors. There is room in the end covers for a three phase bus bar earthing switch.

2.6 DISCONECTORS AND EARTHING SWITCH

     The function of a disconnector in GI switch gear is similar to that of an isolator in the substation yard. The disconnector is of three phase type. The disconnector are of double gap type and can be used for affecting isolation between-

1)      Bus bar system and circuit breaker.

2)      Cable and circuit breaker and

3)      Line and circuit breaker

      The disconnectors form a single gas barrier between the adjacent gas compartments and achieve electrical isolation of the adjacent compartments by means of an electrical interruption of both sides of the gas tight barrier.

      As shown in the fig, in open position the contacts are earthed. As a result an earthed barrier is created between the adjacent compartments of the installation. Because of the safety of the working personal is guaranteed.   

2.6.1 ARRANGEMENT OF DISCONNECTORS

       

       An insulator is located between two compartments and maintains gas seperation fitted in one line. Three rotatable conducting shafts pass through the insulator. In both compartments contact holder are mounded on these shafts .We can see contact fingers fitted on these contact holders. In the closed position these contacts are making contact with the fixed knife on the conductors in the adjacent compartments. Insulating shafts are fitted above the mobile contact holder. By means of the insulating shaft, the conducting shaft together with the contact holders can be rotated during switching through an angle of 180 degrees .In this position, the contact fingers will make contact with the earthing contact on the wall of the compartment. Note that the three phase conductors are situated one above the other in the bus bar and hence the disconnector the fixed knife contacts on the cable termination compartment are fixed in the same level .Here the three disconnector shafts and the three drive shafts are of equal length. Disconnectors are operated by a drive mechanism for which energy is supplied by an electric motor working on 110VDC.  Disconnectors can be operated manually also.

       The insulating shafts are connected to the gas tight bearing bushes in a claw like connections. These bushes are located in the aluminium drive box. Worm wheels are mounted above the bushes, each is driven by a worm. The worm shafts are coupled and on the one side a revolving handle can be fitted. The electric  motor  with gearing is mounted on the same side.By use of handle the safety switches interrupts the motor supply. A system of auxiliary contacts are coupled to the worm wheel away from the motor. The position indication is also mounted on the wheels.

 2.6.2 DISCONNECTOR LOCKING DEVICE        

The diconnector is provided with an electrical/mechanical locking device. When the handle is fitted, the supply to the motor is automatically interrupted. For assembly and maintenance work the disconnector can be locked by attaching the locking plate. Switching is then prevented both mechanically and electrically.

2.6.3 EARTHING SWITCH

        The function of an earthing switch in G.I.S switchgear is to earth a cable, a line or the bus bar to provide safety for the working personnel during tests or maintenance .The earthing switch is also used for earthing parts of the installation during tests. The earthing switch is of three phase, fault making type, that is, it is possible to switch on to a live conductors. The earthing switch can be operated manually or by means of a driving motor operated at 110 VDC and spring mechanism.

        Ref figure, in these three parallel arms with double contact knives are mounted on a 90 degree rotating shaft. In the ‘ON’ position these knives make contact with the receiving contacts on the conductor system in the cable termination unit or bus bar. This active section is mounted in a housing, which is mounted on the cable termination unit or bus bar by means of a rectangular flange connection. One end of the shaft passes through the housing to the outside where it is driven by a motor-reducer/located-spring mechanism.

2.7 LOCAL CONTROL CUBICLE

       A local control cubicle is mounted on the front side of the switchgear foe the various operations and control of the equipment parts. Circuit breakers, disconnectors, earthing switches etc. can be operated from L.C.C.  This is in addition to the operation which normally takes place in the central panel in the operator’s room. Provision for signalling alarm is also given in the Local Control Cubicle.

For example:

·         Position indicators

·         Auxiliary contacts

·         Gas density metering

·         Hydraulic  pressure metering etc

Sometimes alarms are interfered by switching the circuit breaker.

        For example: Gas density metering. This is one of the main alarms connected inside the L.C.C. but due to contact bouncing when a circuit breaker is closed or opened, an alarm may be caused which is not realistic. As a protection against this problem time delay is made in all outgoing gas density alarm signals by adjusting the connecting relay. Contact bouncing can occur in the hydraulic oil metering device also. Hence their contacts also have to be delayed. Since the oil needs more time to stop oscillating, a time delay of 20 seconds is set for the time relay to initiate the alarm. Position indication in the L.C.C. is achieved by using special type of indication where the green indicator will show the open position and the red indicator shows the closed position. Components inside the L.C.C. such as contactors, micro circuit breakers, push button etc are commonly used items only.

2.8 CURRENT TRANSFORMERS AND POTENTIAL TRANSFORMERS

2.8.1 CURRENT TRANSFORMERS

      The current transformers are mounted in the circuit breaker compartment as shown in figure. The function of CT’s are-

·         Metering

·         Line or transformer protection

·         Line or transformer back-up protection

·         Bus-bar protection

       The CT’s essentially consist of primary and secondary coil and core. The magnetic circuit in most cases is constructed in the form of rings with cold grain oriented silicon steel or nickel alloy according to the performance required. Each secondary coil is wound on insulated ring core and insulated primary passes through this ring.

      The insulated primary conductors pass through the porcelain and the primary leads are taken out through small terminal bushings fixed to the side of expansion chamber on the upper end of the porcelain. The secondary terminals are brought out. The terminal rings and terminal box are fixed to the tank.

       Although CT’S in G.I.S. equipments look like a very robust object, it is a valuable high quality instrument. Because the outside of CT is not protected mechanically, the winding insulation can be damaged easily by kicking or dropping the CT. Hence utmost care should be taken at the time of handling of CT.

       Moisture can influence the dielectric property. Moreover aggressive chemical product may be formed from moisture and derivatives and hence a CT is always kept dry.

2.8.2 VOLTAGE TRANSFORMERS

       An inductive SF6 insulated voltage transformer consist of three single phase transformers located in one compartment adjacent to three cable connection compartment. The VT essentially consists of primary and secondary windings such as core and porcelain bushing. For the purpose of gas system, the cable connection compartment is interconnected with the compartment for VT by a tube connector as shown in figure.

        The purpose of interconnection is the mutual control of gas pressure in both compartments. For maintenance work in the cable connection compartment, the value (9) is available to keep the voltage transformer compartment under an over pressure of 0.5 bar SF6. This is usually monitored via a pressure gauge (8) with a maximum of 2 bar between VT and cable connection department. During operation in the substation the handle of the valve must be removed to ensure that the valve is not closed. In that case no control of the pressure and density of the voltage transformer compartment is possible. For cable testing purpose the VT can be disconnected by means of the built in isolating device (5).

The operating sequence of this isolator is:

·         Remove the cover (A).

·         Unscrew bracket (B) from ring C and bracket (D).

·         Remove the bracket (B).

·         Turn the bolt head E in the centre counter-O in front.

·         Fit bracket (B) with the indication-O in front.

·         Connect bracket (B) to the ring and bracket.

·         For bringing into the closed position (“I”) follow the reverse sequence.

2.9 EARTHING OF SUBSTATION

Earthing is to be provided in AC due to the following reasons-

1.   To provide a means to carry electric currents into the earth under normal and fault conditions, without exceeding any operating and equipment limits or adversely affecting continuity of service.

2. To ensure that a person in the vicinity of grounded facilities is not exposed to the danger of electric shock.

The effect of an electric current passing through the virtual parts of a human body depends on

1)       Duration 

2)       Magnitude

3)       Frequency

The following parameters have to be taken into consideration for designing earthing for substations.

(A) RESISTANCE UNDERNEATH THE FEET

The resistance underneath the feet is determined by the following parameters:

1. Resistivity of the ground.

2. Circuit (foot-foot or hand-free).

3. Mutual resistance between foot resistances.

(B)  RESISTANCE OF THE GROUND BENEATH THE FOOT

RFOOT=Q/(4.b)

(C) MUTUAL RESISTANCE BETWEEN THE FEET

   RM FOOT =Q/(2π*dFOOT)

With     Q  :  resistivity of earth [m]

              b   :  equivalent radius of the foot [m]

       dFOOT  :  separation distance of feet [m]

(D) RESISTANCE OF THE HUMAN BODY

Extensive tests also performed showed the following values of the resistance of the human body:

AC resistance from hand to hand: 2330 ohm

AC resistance from hand to (both) feet: 1130 ohm

These values can be increased due to insulation of shoes, dry hands etc.

NOTE : According to IEEE Std. 80

1.      Hand and shoe contact resistances are assumed to be zero.

2.      A value of 1000 ohm is selected for the calculation from hand-to-hand. Hand –to-(both)-feet and foot-to-other-foot

>R B=1000 ohms

(E)  STEP VOLTAGE CIRCUIT

The step voltage circuit is defined by a current flowing from one foot to the other, so that the resistance underneath the feet is placed in series.

The resistance underneath the feet R2FSis given by,

R2FS= 2(RFOOT  - RM FOOT)

Approximately this may be written as

R2FS = 6Q, where Q= resistivity of the earth (ohm meter)

The resistance of the accidental circuit

RA= RB + R2FS

(F)  TOUCH VOLTAGE CIRCUIT

This is defined by a current flowing from both feet to the hands so that the resistances underneath the feet placed in parallel.

The resistance underneath the feet R2FP is given by

R2FP= 0.5 (RFOOT+ RM FOOT)

Approximately, R2FP= 1.5Q

The resistance of the accidental circuit is given by,

RA= RB+ R2FP

(G) FAULT CURRENT

The fault current is the maximum possible current with an appreciable probability. Fault current, IF is given below

IF= 3Io (Io is the symmetrical fault)

Where Io= [E/3] x 1/ [Z1+Z2+Z0+3Ri] for a single line to ground fault with

E   = Nominal system voltage

Z0 = Zero- sequence (subtransient) reactance.

Z1 = positive sequence (subtransient) reactance.

Z2 = Negative sequence (subtransient) reactance.

R1 = Estimated minimum resistance of the fault itself (normally 0).

 Fig. Comparison of conventional substation & GIS substation.

Fig.Over all view of 66KV GIS substation

Fig.Hydraulic system along with CB contact

Fig.SF6 gas filling system

Fig.Sf6 gas monitoring system

Fig.Ring main unit

Fig.Internal view of ring main unit

Fig.Cable termination compartment

Fig.Top view of GIS

2.10 HYDRAULIC PART OF THE DRIVE

2.10.1 HYDRAULIC DRIVE UNIT

       A large number of components such as magnetic valves, control valves, non-return valves, restriction of the main cylinder etc, are integrated in the hydraulic drive unit. The piston rod of the main cylinder is connected to the crank from the central shaft in the drive box. The differential is constructed in a way that it will hydraulically brake at the end of both the close and opening stroke. Restriction in the oil channels makes it possible to adjust the required speed characteristics. There is a single control circuit for switching on (a) and a double control circuit (b, b1) for switching off.

Functioning:

       When the magnetic valves (a,b,bl) are energized the associated servo buster valves (c and d respectively) are opened (“c“ is for closing and “O“ is for tripping of the circuit breaker).As a result of this the bi-stable control valve (e) is placed in the corresponding position. These final positions are maintained on the one hand by a mechanical restraint and on the other by the differential action of the valve. The bi-stable valve operates the ports of the main cylinder, in which a differential position can move (f). Should the oil pressure drop, the circuit breaker is locked in the ON position by locking cylinder (h).

      The drive energy is given by the hydraulic (B) which in turn is kept under pressure by the hydraulic pump unit (C). The pump unit’s motor is activated by one of the pressure switches (5) with a difference of approx. 10bar. The oil is sucked from the tank through a filter and compressed via a non-return valve (2) to the accumulator. The safety valve (1) restricts the pressure to maximum 300bar. The needle valve (3) is used to release pressure for maintenance purpose and is closed during normal operation. A hand-operated pump (6) is mounted in parallel to the electrically operated pump in order to be able to adjust the circuit breaker during maintenance activities.

2.10.2 ACCUMULATOR

      The hydraulic accumulator consists of a high pressure cylinder in which two chambers are separated from each other by a floating position. One chamber is filled with high pressure nitrogen (N2) and the other chamber, which is connected to the hydraulic system, is filled with oil.

      While the hydraulic system is being pressurized the position is driven by the oil, compressing the gas in the other chamber. During a switching-on and switching-off cycle, the oil is driven at great speed by the compressed gas into the drive cylinder. The compressed gas acts as a gas spring.

      The oil volume in the accumulator is sufficient for the completion of complete “O-C-O” cycle, or two C-O cycles. A signalling contact (g) is located on the accumulator to warn of an excessively low gas volume.

2.10.3 HYDRAULIC PUMP UNIT

      The pump unit pressurizes and maintains that pressure in the hydraulic system, including the accumulator. The hydraulic pump is driven by an electromotor. The filters necessary to protect the components from pollutants are located in the pump unit.

The components mounted on the pump unit include the following:

·         Safety valve. This valve restricts the pressure in the hydraulic system.

·         A non-return valve in the pressure line prevents back-flow via the pump when the pump is not operating.

·         A needle valve which act as a by-pass connection to the tank in order to release pressure during maintenance or servicing.

·         Oil-fill gap and level gauges for monitoring the oil level in the tank in the pump unit. The oil level can be read off the level gauge (approx. 40litres).

·         Pump with electric motor.

·         Hand pump for operating the circuit breaker during servicing and maintenance

2.10.4 HYDRAULIC SYSTEM

The three main functions are illustrated in the diagram:

·         Valve block of the drive unit.

·         Hydraulic accumulator.

·         Hydraulic pump unit.

a,b,bl  =  electromagnetic valves for  “C” and “O”

c, d      = servo valves for “C” and “O”

e          = bi-stable control valve

f           = main cylinder

g          = switch for monitoring

h          = locking cylinder

1.      Safety valve       6. Hand pump

2.      Non-return valve   7. Test input

3.       

2.10.5 ADJUSTMENTS

       The hydraulic system operates at a pressure of 232-282 bar and a no of pressure switches monitor and control the mechanism. The switches are set at falling pressure, except for “Pump Off”

(A) Setting level of the pressure switches (±1%)

Switching diagram of hydraulic pressure monitoring system

·         Pump off

·         Locking tripping operation

·         Falling pressure signal

·         Locking closing operation

·         Pump motor ON

·         Safety pressure

2.11 INTERLOCKING

When we discuss the interlocking principles, we have to divide the interlocking into two groups:

·         Safety interlocking;

·         Operational interlocking;

       The main difference between both interlocking is the danger that can occur when a certain interlocking does not exist. Safety interlocking is necessary to give the operator or autoswitching equipment no opportunity to create an internal fault in the GIS system or to create unacceptable operation of equipment. Operational interlocking prevents the operator for switching the GIS in restricted conditions, sometimes defined by the customer or electricity board.

       An example:  High speed earthing switches are designed for closing on a live circuit, i.e. there will be no safety interlocking to prevent this. There can be an operational interlocking between a disconnector and a high speed earth switch, so the earth switch cannot be connected to a live circuit. Unacceptable operation of equipment can be seen as giving a closing command.

2.11.1 INTERLOCKING ON THE GIS EQUIPMENT

The safety interlocking can be divided into two groups:

·         Equipment related interlocking;

·         Gas & hydraulic related interlocking.

        Most equipment interlocking is related to the disconnector because this type of switch is not capable of breaking load, switching is only allowed during equal potential on both sides of the disconnector. Following equipment related interlocking are examples to prevent the GIS for an internal fault or unacceptable operation:

·         The disconnector cannot be operated in intermediate position (intermediate mode disturbance)

·         The disconnectors Q1& Q2 are mutually interlocked, engaged alternately only.

·         The CB cannot be closed when related disconnectores are in intermediate position.

·         The disconnectors  related to a CB cannot be operated when that CB is closed

2.11.2 INTERPANEL INTERLOCKING

        In most substation configurations, the interpanel interlocking is related to two types of interlocking:

·         Inter locking concerning busbar disconnectors in relation to busbar earthing;

·         Interlocking concerning busbar disconnectors  in relation to the bus coupler.

2.11.2.1  THE INTERLOCKING BETWEEN BUSBAR DISCONNECTORS AND BUSBAR EARTHING SWITCHES

       Controlling of the busbar disconnectors of all bays is allowed only when the busbar earthing switch of the related busbar is open . this interlocking can be provided  in two ways:

·          By using a hard contact of the earthing switch for every bay;

·         By using auxiliary relays per bay and only one set of hard contacts.

      The disadvantage of using 1 hard contact per bay is the amount of contacts used for this interlocking. For each panel, one relay per busbar is provided &all these relays are controlled by one contact of the related busbar earthing switch. Because of the safe operation of the relay, i.e the relay is energized in a safe situation, a good interlocking system is provided. The opposite interlocking, interlocking the busbar earthing switch for closing with the related busbar disconnectors, is done by a series connection of the auxiliary contacts of all busbar disconnectors.

2.11.2.2 THE INTERLOCKINGS  BETWEEN BUS COUPLER AND  BUSBAR DISCONNECTORS

       In a normal situation i.e. when the buscoupling is not provided, only one busbar disconnector per bay can be closed. This is to prevent unacceptable busbar coupling. This interlocking is standard in every bay with two busbar disconnectors. However, when a coupling bay is situated inside the substation, it is possible  to create equal polarity on both busbar by closing the coupling bay. In this situation it is allowed to operate both busbar disconnectors of 1 bay.

      When both busbar disconnectors of one bay are closed, it is clear that no opening of the coupling bay is allowed. This opposite interlocking is also available in each bay. This interlocking is looped to the buscoupler bay. The mentioned buscoupler related interlocking is necessary to provide a safe “busbar takeover under load “without a shutdown of a complete substation.

2.12 NITROGEN N₂

      Besides the oil system there is also nitrogen under high pressure (±280 bar), placed in an accumulator. During switching of the CB this N₂ will transfer energy to the oil which now has enough to complete a correct switching operation. Due to leakage of this gas the situation could occur that there is not enough N₂ valid to perform a correct switching operation which can lead to not interrupting the current. To prevent this there are two security levels;

·         First : Signalling low  N₂ (switchgear is still operative)

·         Second : Blocking of electrical operation (opening as well as closing command)

2.13 CONTROLLING CIRCUITS OF THE CB

2.13.1 THE PUMPMOTOR AND ITS HYDRAULIC PRESSURE LEVELS

The main power circuit normally consists of following components:

·         A MCB (F8) for turning of the main power

·         A motor thermal relay(F7)

·         Auxiliary relay contacts of a hydraulic switches controlled contactor (K9).

      The main switch can be a normal switch or a micro CB. It is normal engineering practice to place a thermal relay in the main circuit. Activating of this component will de-energize the control circuit by contact F7 95/96. Normal operation pressure of the CB is between 272 and 282bar. If the hydraulic pressure drops under a level of 272bar, pressure switch S16-1 operates. Thus energizing contactor K9.The pump motor tries to restore the necessary pressure. When the motor is running for more than one minute, there will be an alarm. This alarm is discussed in a separate unit about signaling. When the pump motor is restoring the pressure, at 282bar the pressure switch S17-2 will open, what causes the motor to stop (K9 will de-energize).

      Additional to this control circuit, there are three more metering stages that signal a further dropping pressure. The first stage (262bar) signals the dropping pressure, a indication that the pump motor can’t restore the operational pressure. The two other stages block the CB since passing those stages can’t guarantee a proper operation of the CB. These two stages are called trip lockout (232BAR) and close lockout (240bar).

2.13.2 ANTI-PUMP FACILITIES ON THE CB

      Another very important item in the CB controlling is an anti-pump facility in the open K24 4/14 contact in the main close circuit and the closed K24 3/11 take-over contact in the anti-pumping circuit: when the CB receives a tripping command, the S1 41/42 contact will open again when the CB reaches its open end position, thus ending the anti-pumping facility. The closed K42 3/11 take –over contact prevents the CB for this failure.

2.13.3 THE TWO TRIPPING COILS

      The CB has one closing coil, controlled by a anti-pumping facility. The tripping is done by two separate tripping circuits. Sometimes trip coil supervision is added to this circuit. Hydraulic pressure low stage 2, nitrogen low or SF6 low stage 2 will cause a locking on the tripping circuit by de –energizing an auxiliary relay. the two tripping circuit are included in fig.6

2.14 DISCONNECTORS

      Opening a three phase disconnector provides a safe separation between live circuits and circuits that are switched off for HV testing.this is created by an earthed construction between HV and operating personnel. Also a gas separation is provided in the construction of the disconnector.

2.14.1 SPECIFIC FEATURES

      Automatic earthing of disconnector conductor is done at open position of disconnector. The disconnector is not a load breaker, no live circuits can be operated. The driving mechanism is a servo-motor. substation can remain in service during HV testing.

TECHNICAL SPECIFICATIONS:

·         Short–time current of disconnector contacts to earth : 40KA/sec

Rated current	1600A
Opening time	4 sec
Closing time	4 sec
Driving mechanism	Motor
Power supply	HVdc

2.14.2 AUXILIARY CONTACTS

      The auxiliary contacts in the signaling box are divided in two  groups, the SI contacts and S2 contacts.

      The SI contacts are normally operated when the disconnector is open. Closing the disconnector will immediately change the status of SI from operated to not operated. For this reason, the SI contact is also named “early contact”. The SI contact can be a make or break type, thus creating early make and early break contacts when the disconnector is closed, the S2 contacts will become operated. Between changing the status of S1&S2 there is 4sec, for this reason the S2 contacts are named “late make” & “late break” contacts. The early (A) & late make (B) contacts determine the end position of the disconnector.

Note; The switching diagram shows a little time difference between open &close position of the disconnector and operation of the auxiliary contacts. This is because the auxiliary contacts have a minimum switching time.

2.15 SWITCHES

      One of the components of the L-SEP switchgear is the three phase earthing switch. The earthing switches are incorporated in an installation for having the possibility to earth a cable, a line or a busbar system. The earthing switch is also used for earthing parts of the installation during tests. In following paragraphs, the specific features and the function will be described.

2.15.1 SPECIFIC FEATURES

      The earthing switch is of the fault make type i.e , it is possible to switch on to a live conductor. The insulator construction of the earthing switch is suitable for a test voltage of 2 KV, which makes it possible to perform a variety of measurements on the HV termination.

TECHNICAL SPECIFICATION-

Making current 65KA

Short-time current 40KA/sec

Driving mechanism spring

Operating mechanism motor

Operating voltage 110Vdc

2.15.2 AUXILIARY CONTACTS

The used auxiliary contacts are operated by a rotating shaft with cams on it.

      The S1 contacts are normally operated when the earthing switch is open. Closing the earthing switch will immediately change the status of S1 from operated to not operated. For this reason, the S1 contact is also named ”early contact”. The S1 contact can be a make or break type, thus creating early make& break contacts. When the earthing switch is closed, the S2 contacts will become operated. Between changing the status of S1&S2 there is some time. For this reason the S2 contacts are named “late make”&”late break” contacts. The early break (A)& late make (B) contacts  determine the end position of the earthing switch.

2.16 SIGNALLING & ALARMS ON THE LOCAL CONTROL CUBICLE

On the GIS & its control panel we have several signaling & alarm options. For example:

·         Position indicators;

·         Auxiliary contacts;

·         Gas density metering;

·         Hydraulic pressure metering;

·         Voltage and/or current metering;

·         Annunciators;

·         Discrepancy signaling lamps.

2.16.1 GAS DENSITY METERING AND CONTACT BOUNCING

      Also blocking and sometimes forced tripping are controlled by gas density setting. A problem with gas density metering can be the contact bouncing when a CB is closed or opened. These actions can cause a nonrealistic alarm when no protection is provided. Our protection

against this problem is a time delay on all outgoing gas density alarm signals (3sec). For blocking circuit no time delay is included because the time delay is only operative during the switching of the CB.

      The gas density alarm also needed a time delay when they initiate a forced tripping on the CB. By using time delayed signals, no liquid filled gas density meters have to be used.

2.17 DEFECTS IN GIS INSULATION

     Defects in the insulation system of GIS may be left from the production of the units in the factory and they are generated during the assembly at site, or they may occur during normal operation. Location of the defect is done by searching for the location along GIS with the highest signal level.

Protrusion on earth and live parts:

        A protrusion from live or earthed parts will create a local field enhancement. Such defects will have a little influence on AC withstand voltage because voltage varies slowly, and the corona at the tip will have time to build up a space charge that shields the tip. For impulses like lightning surge or very fast transients produced by disconnector operation, the impulse duration is too short to build such space charge. Consequently the lightning impulse withstand voltage for instance will be heavily reduced due to this type of flaw .Usually protrusion exceeding 1-2mm on the phase conductor are considered harmful l. Due to lower strength a similar protrusion on the encapsulation will be much less severe.

Free moving or fixed particle:

      Free moving particles have little impact on the LIWL (lightening impulse with stand level),while the AC withstand level can be significantly reduced by their presence. The reduction will depend on their shape and position; the longer they are and closer they get to HV-conducer the more dangerous they become. If they move on to the spacer they become even more dangerous.

Voids and defects in spacers:                      

A defect inside a spacer will give rise to discharges, electric stresses and eventually lead to breakdown

Electrically and mechanically lose shields:

       Field grading shield becomes mechanically loose and it may become electrically floating. Floating shield adjacent to an electrode on potential will give rise to large discharges between shield electrodes

Benefits using the AIA-1 to detect and locate flaws in GIS:

       Some of the failure in GIS originates from less suitable designs, but these are continuously being improved. Another group of failures are considered to be of an almost inevitable stochastic nature. These are failures initiated by flaws introduced during manufacturing, assembled at site and during operation. Flashover in a GIS is in general associated with longer outage times and greater cost than in a conventional air insulated substation, and their consequences may be severe.

2.17.1THE “HOT STICK”MEASURING TECHNIQUE:

         Measuring on cable terminations is done with voltage applied during service or as a test after assembly. This requires a measuring technique tested and approved for live work. For this purpose a glass fibre rod is used. The sensor of ALA-1 is mounted in the handle and the acoustic signal is transferred through the glass-fibre stick to the sensor. The measurements are performed by pressing the tip of the glass fibre rod onto the laminations at various positions. The tip is equipped with a soft rubber sphere filled with some sort of grease to obtain good acoustic contact for the signal. Partial discharges in the termination is discovered when the 100(120) Hz signal is high compared to the 50(60) Hz signal. The plot in particle mode (amplitude vs elevation time) gives higher amplitudes and shorter time between discharges as the discharge level increase.

2.18DEMERITS OF GIS

·         High cost compared to conventional outdoor substations.

·         Requirements of cleanliness are very stringent. Dust or moisture can cause internal flashover.

·         Procurement of gas and supply of gas must be maintained.

·         Project needs almost total imports including SF6 gas spares.

·         SF6 leakage may lead to suffocation. Some of the gaseous and solid by –products formed inside G.I.S are hazardous.

2.19 APPLICATIONS OF GIS

.      Switch gear installations for higher security requirements.

·         Indoor switchgear installations with minimum space requirements therefore ,specially suitable for congested areas.

·         Protected installations in areas of contaminations and corrosion by sea or desert climate and in industrial plants.

·         Cavern switch installations for hydro and pump storage power plants.

·         In power plants, with the possibility of accommodation in the immediate vicinity of the transformers to achieve an optimum overall concept.

·         Extension of existing conventional outdoor installations on a limited ground area.

·         Replacement of  existing conventional switchgear installations enabling increased voltage level, without additional space requirements

·         SF6 GAS insulated substations (GIS)

·         Hybrid solution as a combination of metal-enclosed switchgear components together with equipment of conventional design.

·         On hilly terrains.

2.20 POWERLINE CARRIER COMMUNICATIONS

      The 9505 power line carrier (PLC) terminals supplied by BPL Telecom Ltd are intended for the transmission of speech, telemetering, teleprinting, telecontrol, teleindication and teleprotection signals in the carrier frequency range between 50kHz  to 500kHz over the following communication media with suitable line coupling equipments:

High voltage and medium voltage power lines.

Open wire lines exposed to power lines.

Message transmission is based on signal side band (SSB) principle where the carrier power and one of the two sidebands generated as a result of modulation are suppressed.

The advantages of this mode of operations are:

·         Optimum utilization of the available send power for signal transmission.

• Minimum channel width to conserve spectrum space.
• Large transmission range.

       The model 9506 PLC provides single or twin channel voice grade channels for the transmission of speech or audio tones over HV transmission lines. The 9505 PLC terminals are available in 4 configurations -9505HP,9505IP,9507LP,and 9505SP.The 9505HP configuration equipped with a 40W amplifier  (95AMP-HP) which feeds the programmable line filter (95PLF-HP) is installed in the GIS .It utilizes only one channel from the two available.

        Coupling mode: The AF coupling mode is adopted for back coupling of 95PLC terminals .Here he terminals are inter connected at AF level

2.20.1 OPERATING PRINCIPLE

        9505 PLC consists of the following sections: AF section, IF/HF section and HF line section. The AF section on the send side includes input circuit telephony, dial signal generations circuits be transmitted .These are speech input circuit telephony, dial signal generation circuits for dialing and pilot signal. On the receiving side, the AF section has corresponding output circuits which separate out different signals like speech, dial etc. In order to connect telephone through automatic relay equipment or PAX, AF hybrid is provided for speech and for 4 wire /2wire conversion.9505PLC incorporates a speech interface (95PIN) circuit and a data interface 95(DATA) circuit. The 95MODEM is the heart of the 9505PLC system and comprises IF/HF section for both transmit and receive side.

       The AF signals are converted into IF signals using the IF carrier of 5.12 MHz generated in the system using a crystal oscillator .In the transmit section, the IF band is filtered out using a 10 pole crystal filter and fed to a final mixer stage. The carrier required for mixing is derived from a voltage controlled oscillator (VCO).The mixer output is HF signal in the range of 50kHz to 500kHz in steps of 0.5kHz.In the receiver section, a VCO generates the requires demodulating carrier and IF band is filtered using a crystal filter. IF to AF demodulation is achieved by using 5.12 MHz as the carrier.

        Automatic gain control (AGC) is built unto the demodulator section regulate AF output for variation in HF input. The HF line section on the send side has an RF power amplifier to provide high power of transmission at the terminal output.

2.20.2 FUNTIONAL DESCRIPTION:

The 9505-HP PLC is provided with the following modules

Power Supply Unit (95PSU-HP):

       This provides regulated +/- 12V DC and unregulated +/- DC outputs .The unregulated outputs are used to power the output amplifier stages .95PSU-HP is powered by a 48V dc. Voltage regulation for +/-12V section is achieved through 3 pin regulators. Input over voltage protection is also provided, the voltage detected by an SCR.       

Speech Interface (95sPIN):

        This module is the interface from the speech circuits to the 95MODEM .Interface is provided for telephone,2 wire express telephone,34 wire express telephone and lack telephone communications. The jack telephone and 4 wire express telephone act as parallel channels. This also contains ton – generating circuits for signaling and alarm indication and speech equalizer.

2.20.3 MODULATOR/DEMODULATOR(95MODEM)

        This module contains two basic sections, a modulator that converts audio signal in to a single side band (SSB) signal and a demodulator that converts a  received SSD signal back into an audio signal. Both sections use a 5.12MHz interface frequency (IF) signal are completely independent in their operation. A crystal oscillator in the demodulator section provides reference frequency for some circuit in the modulator section.

       Modulator section is a single conversion heterodyning transmitter with an If of 5.12MHz.it produces a double side band (DSB) signal, which is converted to SSB using filtering techniques. This modulator section comprises of a synthesizer ,a speech amplifier, a high pass filter, a compressor/amplifier ,an active low pass filter, a balance modulator .an IF filter, a mixer, an RF output amplifier, and a signaling transmitter.

       The output of speech amplifier is given to a high pass filter where low frequency components of the speech signal are limited so as to prevent spurious output near the carrier. An operational amplifier can configure itself as a signal compressor or amplifier depending on the ON/OFF signal it receives. If this signal goes low, the OPAMP function as a compressor and if it goes high it functions as amplifier. Active low pass filter is used to suppress all speech signal above a specific frequency to prevent interference with the data channels and signaling tone produced by signaling transmitter. Balanced modulator accepts signals from active low pass filter and signaling transmitter. It uses this signal to generate 5.12MHz signal with DSB s and a suppressed carrier. IF filter suppresses the upper side band (USB) of balanced modulator output. The demodulator section is a single conversion receiver that uses the same 5.12MHz IF as in the modulator section and converts the SSB into audio section .It contains a crystal oscillator, a synthesizer, an input low pass filter, an input mixer, an IF amplifier, a product detector, a speech channel low pass filter, an expander/output amplifier, an FSK band pass filter, a signaling receiver, an audio gain control circuit and signal to noise ratio alarm,

      Crystal oscillator generates reference frequency for synthesizer in both sections of 95MODEM. Synthesizer set the frequency at which demodulator section will receive inputs. Input mixer converts its input signal into 5.12 MHz IF by combining it with the output of synthesizer and send it to IF amplifier .The output of IF amplifier is fed to product detector where the signal is combined with 5.12MHz crystal oscillator output to produce audio output signal. The output of product detector is fed to audio transformer which splits the signal into two parts. The first part is fed to OPAMP to produce speech plus output and the other part is fed to input of speech channel.

CHAPTER 3

CONTROL AND PROTECTION

3.1PROTECTION

      Modern power systems are growing fest with more generators, transformers and large network in the systems. For system operation a high degree of reliability is required. In order to protect the system (lines and equipment) a form damage due to undue current and /or abnormal voltage caused by faults (such as short circuit) the need for reliable protective devices, such as relays and circuit breakers arises. The most common electrical hazard against which protection is required at the short circuit. However there are abnormal conditions – e.g., overloads under-voltage and over-voltage, open phase, unbalanced phase currents reversal of power, under-frequency and over-frequency, over-temperature, power swings.

      On the occurrence of short circuits which may lead to heavy disturbances in normal operation damage to equipment, impermissible drop in voltage etc the protective scheme is designed to disconnect or isolate the faulty section from the system without any delay. The protective scheme is designed to energize an alarm or signal whenever the overload and short circuit do not present a direct danger to the faulted circuit element and the entire installation .for example, an occurrence of a single phase fault to earth in overload circuits take the necessary measures for removal of the abnormality and prevent any interruption in power supply to consumers.

        The main functions of protective relaying are to detect the presence of faults, their locations and initiate the action for quick removal from service of any element of power system when it suffers a short circuit or when it starts to operate in any abnormal manner that might cause damage or otherwise interface with effective operation of the rest of the system. The relaying equipment is added in this task by the circuit breakers that are capable disconnection the faulty element when they are called upon to do so by the relaying equipment.

3.1.1    OPERATION OF PROTECTIVE EQUIPMENT

      The protective relays connected in the secondary circuits of current transformers and/or potential transformers. Under normal operating conditions, the voltage induced in the secondary of the current transformers is small and therefore current flowing in the relay operating coil is insufficient in magnitude to close the relay contacts. This keeps the trip coil of the circuit breaker de-energized. Consequently the breaker contact remains closed and it carries the normal load current. On occurrence of fault a large current flows through the primary of the current transformer. This induces the voltage induces the secondary and hence the current flowing through the relay operating coil .The relay contact are closed and trip the coil of the breaker gets energized to open the breaker contacts .The circuit breaker open its contacts . An arc is drawn between the contact as they separate. They arc is extinguished at a natural current zero of the ac wave by suitable medium and technique. After final arc extinction and final current zero, a high voltage wave appears the circuit breaker contacts tending to re establish this arc. This comprises a high frequency transient component superimposed on a power frequency recovery voltage. These phenomena have a profound influence on the behavior of the circuit breakers and the associated equipment.

3.2 TYPES OF PROTECTION

         In a GIS substation the protection is much more superior when compared to conventional substation. Mainly the protection to be provided is of two types namely

·         Feeder protection

·         Transformer protection

The above can be explained as follows.

3.2.1    FEEDER PROTECTION

        This protection is given for the different components in the feeder bay. The feeder bay includes the incoming feeder and outgoing feeder. The different types of feeder protection are-

·         Backup Protection

a)      Over current protection

b)      Earth fault protection

·         Distance protection

·         Pilot wire protection

3.2.1.1 BACKUP PROTECTION

       Vary frequently ,for attaining high reliability ,speed up action and improvements in operating flexibility of the protection scheme, the separate element of a power system ,in  addition to main of primary protection ,are provided with a backup protection . The protection is the first line of defense and ensures quick-acting and selective clearing of faults within the boundary of the circuit section of an electrical installation. Backup protection is the main given to a protection which backs up the main protection whenever the latter fails in operation, is cut out for repairs etc.

        Backup protection is important to the proper functioning of a good system of electrical protection since percentage reliability not only of the protective scheme but also of the associated current transformers, power transformers and circuit breakers cannot be guaranteed. It is the second line of defense which functions to isolate a faulty section of the system in case the main protection fails to the following reasons

·         The dc supply to the tripping circuit fails

·         The current or voltage supply to the relay fails

·         The tripping mechanism of circuit breaker fails

·         The circuit breaker fails to operate

·         The main protective relay fails

Backup protection consist of two type of protection. They are overcurrent and earth fault protection.

OVERCURRENT AND EARTH FAULT PROTECTION

         The general practice is to employ a set of two or three overcurrent relays for protection against phase-to-phase faults and a separate overcurrent relay for single line –to-ground faults .Separate earth fault relays are employed because they can be adjusted to provide faster and more sensitive protection for single line-to-ground faults that can be provided by the phase relays.

       An induction type overcurrent relay giving inverse time relation with a definite minimum time characteristic is employed for protection .It consist essentially of an ac energy meter with mechanism with slight modification to give required characteristics. The relay has two electromagnets. The upper electromagnet has two winding. One of these primary and is connected to the secondary of the current transformer in the line to be protected and is tapped at intervals. The tapings are connected to a plug setting bridge by which the number of turns in use can be adjusted, thereby giving the desired current setting. The plug bridge is arranged to sections of tappings to give over-current range from 10% to 70% or 20 to 80% in steps of 10% The values assigned to each tap are expressed in terms of percentage of full-load rating of current transformer with which the relay is associated and represents and value above which the disc commences to rotate and finally closes the trip circuit. Thus pick-up current the rated secondary current transformer multiplied by current setting. Adjustment of setting is made by inserting a pin between the spring loaded jaw of the bridge socket at the tap value required. When the pin is withdrawn for the purpose of changing the setting value while the relay in service, the relay automatically adopts higher setting, thus the current transformer's secondary is not open circuited.

       The second windings is energized by induction from the primary, and is connected in series with the winding on the lower magnet. By this arrangement, leakage fluxes of upper and lower electro-magnets are sufficiently displaced in space and phase to set up a rotational torque on the aluminium disc suspended between the two magnets, as in the shaded pole induction disc motor. This torque is controlled by the spiral spring and also sometimes by a permanent magnet brake on the disc. The disc spindle carries a moving contact which bridges two fixed contacts when the disc has rotated through a pre-set angle. The angle can be set to any value between 0° and 360° and thereby giving desired time setting. This adjustment is known as time-setting multiplier. Time multiplier setting is generally in the form of an adjustable back-stop which decided the arc length through which the disc travels, by reducing the length of travel, the operating time is reduced. The time setting multiplier is calibrated from 0 to 1 steps to 0.05.

        Each fault current depends on the type of neutral earthing, i.e., whether solidly earthed, insulated or earthed through some resistance or reactance. Where no neutral point is available, grounding transformer is employed. The earth fault current will be small as compared as phase fault currents in magnitude. The relay thus connected for earth fault protection is different from the ones provided for phase-to-phase faults.

       Here two inverse definite minimum time type overcurrent relays are connected in two phases through CT's and one earth-fault relay. In case of phase-to-phase faults or overload the IDMT relays trip the CB. Under healthy conditions, the sum of all the three currents of CT's is zero and the earth-fault relay remains inoperative. As soon as phase-to- changes fault occurs unbalancing in currents causes the earth- fault relay to operate, which in turn trip the circuit breaker.

3.2.1.2 DISTANCE PROTECTION

      Distance protection is the name given to the protection, whose action depends upon the distance of the feeding point to the fault. The time of operation of such a protection is a function of the ratio of voltage and current i.e., impedance.

      Distance relays differ in principle from other forms of protection in that their performance is not governed by the magnitude of the current or the voltage in the protected circuit but rather on the ration of these two quantities. Distance relays are actually double actuating quantity relays with one coil energized by voltage and the other coil by current. The current element producers a positive or pick-up torque while the voltage element producers a negative or rest torque. The relay operates only when the V/I ratio falls below a predetermined value. During a fault on a transmission line the fault current increases and the voltage at eh fault point decreases. The V/I ration is measured at the location of CT's and PT's. The voltage at FT location depends on the distance between PT and the fault.. If the fault is nearer, measured voltage is lesser and if the fault is farther, measured voltage is more. Hence assuming constant fault impedance each value and the fault along the line. Hence such protection is called the distance protection or impedance protection.

      Distance protection is non- unit type protection, the protection zone is not exact. The distance protection is high speed protection and is simply to apply. It can be employed as a primary as well as back- up protection. It can be employed in carrier aided distance schemes and in auto-reclosing schemes. Distance protection is very commonly used in protection of transmission lines.

       Distance relays are used for both phase fault and ground fault protection and they provide speeds for cleaning faults than over- current relays. Distance relays are also independents exchanges in magnitude of the short- circuit currents and hence they are not much affected by changes in the generation capacity and the systems configuration. Thus they eliminate long clearing times for fault near the power sources required by over- current relays if used for the purpose.

     Here we use impedance type distance relay. An impedance relay is a voltage restrained current relay. The relay measures impedance upto the point of fault and gives tripping if this impedance is less than the relay setting impedance. Relay settings impedance is as replica impedance and it is proportional to the set impedance i.e. impedance upto the reach of the relay. The relay monitors continuously the line current though current transformer and the bus voltage through PT and operates when the V/I ratio falls below the set value.

3.2.1.3 PILOT WIRE PROTECTION

     The time "Pilot" means that between the ends of a transmission line there is an interconnecting channel of some sort over which information can be conveyed. Three different types of such a channel are presently in use, and they are called "Wire Pilot" "Carrier - current pilot" and "Microwave Pilot". The differential pilot- wire protection is most satisfactory and is widely employed on account of the advantages such as simplicity, flexibility, a high stability ratio, and rapid fault clearance.

      The differential pilot- wire protection is based upon the principle that the currents compared at each end of the line or feeder by the use of pilot wires should be same under normal operating conditions and the equality is lost only when there is a fault in between the two ends. The systems is quite similar to that employed for the protection of alternate and transformers and the difference lies only in the length of pilot wires.

3.2.2 TRANSFORMER PROTECTION

This protection is given for different components in the transformer bay. The different types of transformer protection are

• Over Current Protection

• Earth Fault protection

* Different Protection

• Restricted Earth Fault Protection

3.2.2.1 DIFFERENTIAL PROTECTION

       Differential protective relaying is the most positive in selectively and in action. It operates on the principle of comparison between the phase angle and magnitude of two or more similar electrical quantities. A differential relay is defined as the relay that operators when the phasor difference of two or more similar electrical quantities exceeds a pre-determined amount. This means that for a differential relay, it should have (i) two or more similar electrical quantities and (ii) these quantities should have phase displacement for the operation of the relay. Almost any type of relay, when connected in a certain way, can be made to operate as a differential relay. Most of the differential relays are of "Current differential" type in which phasor difference between the current entering the winding and current leaving the winding is used for sewing and relay operation.

      Differential protection relaying is generally unit protection. The protected zone is exactly determined by the location of CT's or PT's. The phasor difference is achieved by suitable connection of secondaries of CT's or PT's.

3.2.2.2 RESTRICTED EARTH FAULT PROTECTION

       Earth fault relays connected in residual circuit of line CT's provide protection against earth faults on the delta unearthed star- connected windings of power transformers. A CT is fitted in each connection to the protected and the secondaries of CT's are connected in parallel to relay. Ideally, the output of the CT's is proportional to the sum of zero sequence currents in the line and tae neutral earth connection if the latter is within the protected zone. For external faults zero sequence currents are either absent or sum to zero in the line and neutral earth connection. For internal faults, the sum of zero sequence currents is equals twice the total fault current.

       If an earth fault occurs near the neutral point of the transformer the voltage available for driving earth fault current is small. For the relay to sense such fault it has to be toe sensitive and would, therefore operate for spurious signals, extern^ fault current of the order of 15% of rated winding   current. Such settings restricted portion of the windings. Hence the name restricted earth-fault protection.

3.3 ADVANTAGES OF STATIC RELAYS

·         The excellent reliability of electronic components enables a very good behavior of protection systems under severe environments. .

·         100% security of operation even after several years of service without any change in characteristics. . 

·         Returning percentage is equal to / greater than 95%.

·         Accuracy is more than 5% even in worst case.

·         100 percentage security of operation even on saturated CT conditions which is fundamental in over current protection of HV networks. . 

• The cut out area required is only 176^th of that of equivalent electromechanical relays available in India. Hence, more relays can be accommodated in the same panel.
• The relays are very compact and look elegant.
• Weight and volume is less.
• Operates faster than conventional electromechanical relays which bring in a real advantage when complex functions are used. Grading time considerably reduced.
• Relays will operate satisfactorily within the range of 80-110% of auxiliary supply voltage.
• Relays have got wide range of settings and are easy to set.

·         Very low burden allowing a large number of parallel functions on the same CT.

·         Complete passivity to mechanical and climatic environment.

·         The relays operate trouble free at ambient temperatures ranging from -5 to +55 degree centigrade.

·         Secondary of CT's are automatically shorted on removal of relays from the cases.

·         Relays form rewired modular protection systems which are l00% factory tested.

3.4 TYPES OF RELAYS EMPLOYED FOR PROTECTION AND CONTROL

3.4.1 THREE PHASE  BIASED  DIFFERENTIAL  PROTECTION FOR  POWER TRANSFORMERS AND GENERATOR TRANSFORMERS

FEATURES:

• Three phase biased differential relays for protection of two winding or three winding transformers.

• No interposing CT's needed. Easy phase angle and current amplitude compensation by selector switches.
• Percentage characteristics ensure high stability during through faults.
• Adjustable minimum threshold setting of 20% to 80% IR which avoids unwanted tripping due to CT errors, tap changing and magnetizing current when operating off- load.
• Magnetizing current inrush restraint.
• Over - excitation restraint by desensitization of minimum threshold.
• Fast operating time   less than 40 milliseconds.
• Indication of faulted phase by Light Emitting Diodes (LED).
• Indication of fault - differential or high-set instantaneous.
• Independent adjustment between the percentage threshold and minimum threshold.
• Test points on the front face for verifying the connect Tons and the settings when the equipments put into service.
• Easy integral test facility to check proper functioning of the internal circuits of the relay by a test push-button on the front panel.

MODELS AVAILABLE

TDTA     3                                                                  3                                                                                                                                                           

Number of windings (2 or 3).

Number of phases (1 or 3).

                                       

               

                          

                            

APPLICATION

        The differential relay type is designed for the protection of transformers against internal short circuits, short circuit between phase and short circuit between phase and earth. It is suitable for the protection of two or three winding power transformers, auto-transformers or generator transformer units. Generally no interposing current transformers are needed together with the relay. The phase angle and current magnitude compensation are carried out with selector switches on the relay front plate.

DESCRIPTION

            The three phase protection assembly is housed in flush mounted case which is a standard 19” international rack, of height 196mm, width 482.6mm and depth from the flush mounting surface is 320mm.The assembly comprises of plug- in cards closed at the front by an anodized aluminium name and transparent poly–carbonate cover.

The front face consists of-

• One two position switch for current magnitude compensation
• (1,1//3) per winding
• One two position switch for phase angle(01) compensation
• (0+120 degree)per winding
• One two position switch for phase angle (02) compensation (0,+180)per winding
• (Total phase compensation equal to (01)+(02)+30degree for delta connected internal CT’s and (01)+(02) for star connected internal CT’s)
• A series of 4mm dia. test terminals for checking the primary and secondary currents, different current and through current.
• One switch per winding for transformer ratio matching on HV and LV sides from 0.6 to 1.26 In steps of 0.06 associated with a two position switch for the fine adjustments 0,+0.03In.
• Minimum threshold current setting for each phase from 20% to 00%IR in steps of 20%.
• Percentage slope setting for each phase from 12.5% to 50% in steps of 12.5%
• 3 LED’s with memory for indication of the faulted phase
• One push button for resetting the LED’s
• One push button per winding to check the electronics circuit with associated two LED’s per phase to indicate minimum operating threshold and high set threshold operation.
• The relay case incorporates a terminal block for external connection with 28 terminations

3.4.2 HIGH IMPEDANCE OVERCURRENT RELAY

FEATURES

·         Solid state design.

·         Designed for tropical environment.

·         Self contained relay.

·         Dimensions comply with international standards.

·         Automatic shorting of C.T. inputs when modules are withdrawn.

·         Built in test facility.

·         Low burden.

·         High speed of operation.

APPLICATION

TDZA relays associated with resistors ensures the selective protection of

·         Bus bars against phase to phase and phase to earth faults.

·         Transformers with an earthed neutral (restricted earth).

·         MV network against phase to earth faults.

• Rotating machines.

CONSTRUCTIONAL FEATURES

       The TDZA relay is housed in a TROPIC PLUS, size 4 case, closed at front by a scalable transparent cover.  Conventional series dropping power supply is employed, and the heat I generating components in the power supply are mounted in a ventilated metallic enclosure at the rear side of the case. The input and output connections are terminated on a terminal block with 28 terminals. The terminal block has CT shorting facility. Current settings are done by means of movable plug in jumper. The plug out positions of the jumper corresponds to maximum setting value. LED indicates operation of relay and can be reset by "RESET" push button. Built in test facility is provided to check healthiness of electronic circuits by pressing "TEST" pushbutton.

GENERAL DESCRIPTION

Relay code:

T    -    Tropicalised

D    -    Differential operation

Z    -     High impedance

A    -    Current operated

MODELS AVAILABLE

Description	Relay type	No of  O/P relays	Case size
Single phase high impedance overcurrent relay	TDZA 10	1	4
Three phase high impedance overcurrent relay	TDZA 30	1	4

When the fault current exceeds the set value threshold detector generates the output signal instantaneously. External resistor is used for an excellent stability of the protection zone.

3.4.3 HIGH SPEED TRIPPING RELAY TYPE: TMTG

APPLICATION

      High speed tripping relay (TMTG) is .used for those applications where short time is essential for tripping of breakers in a protective scheme.

MAlN FEATURES

• High speed of operation.
• Any number of NC or NO or C/0 contacts can be provided as per customer specification.
• Charter free operation.
• LED Flag indication.
• Electrically hand resettable facility.
• Optional self reset contacts can be provided.

GENERAL DESCRIPTION

       TMTG Relay basically consists of a miniature attracted armature type relay module with 3 C/0 contacts. This unit is self .held by its own contact and the same is used to energize an LED indication. The resetting facility is achieved by an N/C contact push button by operation of which breaks the mains auxiliary supply to the relay. For additional contacts attracted armature type relay modules with 2 C/0 contacts are used along with the above 3 C/0 relay module. Numbers of contacts possible are 2, 4 or 6.

NOMENCLATURE

TMTG        X      !   — — — — >     S       Self reset.

COIL RATINGS

Standard coil ratings are given below along with unit consumption.

CASE AND FINISH

TMTG relay is housed on a tropic plus size 4 case ,closed at fronn by a selable transparent cover. Conventional series dropping power supply is employed and heat generating components is the power supply are mounted on a ventilating metalilic enclosure at the rear side of the case.The input and output connections are terminated on terminal block wth 28 terminals.

3.4.4 INVERSE TIME OVERCURRENT OR EARTH FAULT RELAYS

FEATURES

·         Solid state design

·         Designed for tropical environment.

·         Self contained relay.

·         Automatic shorting of CT inputs when modules are withdrawn.

·         Built in test facility.

·         Low burden.

·         Wide range of current settings.

APPLICATION

a) Network Protection

Inverse time overcurrent relay allows network protection against overcurrents, short circuits and against fault between phase and earth.

 b) Machine Protection

These relays protect alternators and motors against short-circuit and overloads.

CONSTRUCTIONAL FEATURES

      The TSA relay is housed in a TROPIC PLUS, size 4 or 5 case, closed at front by a sellable transparent cover. Conventional series dropping power supply is employed, and the heat generating components in the power supply are mounted in a ventilated metallic enclosure at the rear-side of the case. The input and output connections are terminated-on a-terminal block with 28terminals .the terminal block has CT shorting facility.

      Current settings (both time delayed (IR) and instantaneous (ISI) and time setting is done by means of movable plug in jumpers The plug out positions of these jumpers corresponds to maximum setting values. High set unit inactive when jumper is in 'oo' position. A fine adjustment potentiometer is provided for intermediate time setting. LED's indicate operation of reply and can be reset by 'RESET' push button. Built in test facility is provided to check _Of electronic circuits by pressing 'TEST' push button.

 GENERAL DISCRIPTION

a)RELAY CODE

 T - Tropicalised

S - Inverse characteristics

A - Current operated

SCHEMATIC OF TSA311 RELAY

When fault current exceeds the set value the IDMT characteristic curve is initiated. The output signal is sent to the o/p relay, after the time delay, as per IDMT curve. Whenever instantaneous feature is employed an independent threshold detector generates the output signal when fault current exceeds the set value ( Is ).

3.4.5 HIGH SPEED TRIPPING REPAY TYPE "TMIG"

APPLICATION

High speed tripping replay (TMIG) is used for those application where short contacting time is essential for tripping of breakers in a protection scheme.

MAIN FEATURES

• High speed of operation
• Any number of NU or c/o contacts can be provided as per customer specification.
• Chatter free operation.
• LED flag indication.
• Electrically hand resettable facility.
• Optional self reset contacts can be provided.

GENERAL DESCRIPTION

       TMIG replay basically consists of miniature attracted type relay modules with 3 C/O contacts. This unit is self held by its own contact and the same is used to energize an LED indication. The resetting facility is achieved by an N/C contact push button by operation of which breaks the mains auxiliary supply to the relay. For additional contacts attracted armature type replay modules with 2 C/O contacts are used along with the above 3 C/O relay modules. Number of contacts possible are 2,4 or 6.

X

NOMENCLATURE

TMIG      --------->S--------> self reset contacts

COIL RATINGS

Standard coil ratings are given below along with unit consumption

CONSUMPTION	DE-energized relays     surplus per operating   relay
	>D.C 24V                        0.7W                  2W 30-32V                     1W                    2W 48V                           1.2V                   2W 60V                          1.5V                     2W 110-125V                  3.5W                  2W 220V                           4W                     2W 250V                           4.5W                   2W
	A.C 127-220V                  4VA                      2VA 220V/380V                 4VA                     2VA

OPERATING TIME

Less than 12 ms at rated voltage

Contacts switching capacity

INSULATION

            The relay will withstands a 2.5 KV a.c rms 50Hz one second between all circuits and the case between all circuits not intended to be connected together .It will also withstand 1.25KV a.c. rms 50Hz for one second between matching contacts in open position.

CASE AND FINISH

     TMIG relay is housed in a TROPIC PLUS size 4 cases, at front by a sealable transparent power. Conventional series dropping power supply is employed and the heat generating components in the power supply are mounted a ventilating metallic enclosure at the rear side of the case. The input and output connections are terminated on a terminal block with 28 terminals

3.4.6 TRIP CIRCUIT SUPERVISION RELAY, TYPE: TTSG

FEATURES

• Solid state technology.
• Low burden.
• Continuous supervision with breaker open or closed.
• High frequency disturbance & impulse voltage withstands.

APPLICATION

Trip circuit supervision relay type TTSG provides continuous of the circuit breaker initiating audible and visual alarms in the event of the failure in the trip circuit or the mechanism. Supervision is provided for the trip supply, trip circuit wiring, trip coil and the tripping mechanism of the breaker.

DESCRIPTION

The relay type TTSG consists of two separate for post-close and pre-close supervision. Both circuits offer complete supervision as follows. The output replay is normally energized in a healthy system by drops off:

•   If the trip supply is lost or falls below approximately 80% of the normal voltage.

•   If the trip coil or trip circuit wiring is open circuited.

•   In case of failure of circuit breaker tripping mechanism.

A time delay of about 400ms on drop-off is built into the circuit to prevent false operations due to momentary voltage dips caused by faults in other circuits or during a protection trip. Two pairs of changeover contacts are provided for initiating audio-visual alarms. An operation indicator with memory is also provided on the relay. No external current limiting resistors are required. The relay offers a very high leakage resistance in the trip circuit.

CASE

TTSG relay is housed in a TROPIC PLUS size 4 cases, closed at front by a scalable transparent cover conventional series dropping power supply is employed, and the heat generating components in the power supply arc mounted in a ventilated metallic enclosure at rear side of the case. The input and output connections are terminated on a terminal block with 28 terminals.

3.4.7 AUXILARY RELAY TYPE ‘TAVG'

APPLICATION

TAVG relays are generally used wherever contact multiplication are required The main application of these relays are multiple control and annunciation circuits where reliability and high speed of operation are essential.

FEATURES

·         High speed of operation.

·         Any number of NC or NO or C/O contacts can be provided

·         Chatter free operation.

·         LED Flag indication.

·         Electrically hand resettable facility

·         Optional self reset contacts can be provided

GENERAL DESCRIPTION

      TVAG relay basically consists of TEC relay modules with 3 C/O contacts per pole.The resetting facility is achieved by an NC contact push button which breaks the main auxiliary supply to the relay.

NOMENCLATURE

X

X

E Hand reset contacts S Self reset contacts

 TAVG

No. of elements (1,2, 3, or 4)

COIL RATINGS

Standard coil ratings are given below along with unit consumption

CONSUMPTION	Range                  surplus per operating relay
	>D.C 24V                                          2W 30-32V                                      2W 48V                                            2W 60V                                             2W 110-125V                                    2W 220V                                            2W 250V                                            2W
	A.C 127-220V                                      2VA 220V/380V                                    2VA

Relays operate exactly between 50% and 120% of rated voltage.

OPERATING TIME

Less than 12 ms at rated voltage

CONTACT CAPACITY

                                                                                           OPENING              CLOSING

                                                                                    ------------------------------------------------------

AC (220V-50Hz, cos 0.6)                                                      5A                             8A

DC (135 Vcc-L/R=30ms)                                                      0.25A                        3.5A

                                                                                     -----------------------------------------------------

Continuous                                                                                                  8A

INSULATION

The relay will withstand 2.5 kv ac r.m.s 50Hz for 1 sec between all circuits and the case and between all circuits not intended to be connected together. It will also withstand 1.25kv ac r.m.s 50Hz for 1 sec between matching contacts in open position.

CASE AND FINISH

TVAG relay is housed in a TROPIC PLUS size 4 cases, closed at front by a scalable transparent cover conventional series dropping power supply is employed, and the heat generating components in the power supply arc mounted in a ventilated metallic enclosure at rear side of the case. The input and output connections are terminated on a terminal block with 28 terminals.

*    *    *    *    *

CHAPTER 4

DESIGN OF 110KV GIS SUBSTATION

4.1 EXISTING ELECTRICAL SYSTEM OF KSEB IN KOLLAM CITY

The power requirements of Kollam city is provided by four substations namely

(1)    Ayathil                                                    -66kv

(2)   Kavanadu                                                 -110kv

(3)   Kundara                                                   -220kv

(4)    Kottiyam                                                 -110kv

The electrical section of kollam corporation is divided into eight sections. They are

(1)   Cantonment

(2)   Kadappakada

(3)   Olai

(4)   Thangasseri

(5)   Sakthikulangara

(6)   Pallimukku

(7)   Ayathil

(8)   Killikollur

4.2 LOAD ANALYSIS OF KOLLAM CITY IN THE LAST TWO CONSECUTIVE YEARS

The average load taken by each 11kv on the year 2005&2006 are given below.

PLACE		2005	2006
1.	HEAD POST OFFICE	179.92A	187.64A
2.	KOCHU PILAOAM MOOD	188.25A	186.54A
3.	PARVATHI MILL	160A	166.36A
4.	POWER HOUSE	115A	126.27A
5.	CHINNAKADA	169A	173.36A
6.	KADAPPAKADA	181A	177.1A
7.	S.N.COLLEGE	94A	122.18A

4.2.1 CONNECTED LOAD STATEMENT OF CONTONMENT SECTION.

Domestic consumers                                              =8969KW

Commercial light & fans                                        =3771 KW

Commercial heat &

Small power including 3 HP                                   =8011W

Cinema                                                                    =2648KW

LT Industrial power

a)      Below 15 KW                                             = 4252KW

b)      B) above 15 KW                                         =1242KW

HT consumers

Above 50KW                                                          =2775KW

Lift Irrigation

a)      Below 15 KW                                             =1000KW

b)      Above 15 KW                                             =447KW

Public water works

LT supply                                                                       =121KW

HT supply                                                                      =6416KW

TOTAL                                                                          =39652KW

4.2.2 CONNECTED LOAD STATEMENT OF KADAPPAKADA SECTION .

Domestic consumers                                                      =8969KW

Commercial light & fans                                               =3771 KW

Cinema                                                                           =2648KW

LT Industrial power

4.3 DESIGN OF TRANSFORMER

Total connected load for Cantonment section               =39652KW

Total connected load for Kadappakada section             =21390 KW

Total connected load                                                      =39652 + 21390

                                                                                        =61042 KW

30% of future expansion                                                =20% of 61042

                                                                                        =73250KW

Total load in KVA                                                          =73250/pf

Here we assume pf                                                          =0.8

                                                                                        =73250/0.8 =91563KVA

Taking demand factor                                                     =91563/0.8 =114454 KVA

Taking diversity factor                                                    = 114454/2 =57227KVA

                                                                                        = 57.227MVA

                                                                                        =60MVA

So we are taking 3 transformers of capacity 20MVA each.

The rating of the transformer is 110KV/1kv 20MVA power transformer

4.4 FAULT LEVEL CALCULATION

Assuming base MVA as 100

Base impedance                                                                     = (base MVA×100)/(fault MVA)

Choose high value of fault MVA for design. Therefore take 1124MVA

Base impedance                                                                     = (100×100)/1124

                                                                                               =8.89%

Total resistance/KM                                                              =0.046Ω/KM

Total resistance for 7.2KM cable                                          =7.2×0.046Ω

                                                                                               =0.3312Ω

%line reactance of 7.2KM cable = (line reactance × base MVA)/(KV)²

                                                                                               = (0.3312×100)/ (110)²

                                                                                               =0.0027%

Total % impedance at 110KV                                               =8.89+0.0027

                                                                                               =8.8927%

Fault MVA = (baseMVA×100)/(total %impedance upto the point)

                                                                                               = (100×100)/8.8927

                                                                                               =1124.52MVA

Fault current at 110KV bus                                                   = (1124.52×10⁶)/ (Г3×110×10³)   

                                                                                               = 5.9KA

% Impedance of 110KV, 20 MVA transformer,

% Impedance at base MVA                   = (% impedance at rated MVA ×base MVA)/rated MVA

                                                                                                = (10×10)/20

                                                                                                =50%

Three transformers of 20 MVA are connected in parallel

 Total % impedance                                                                = 1/z =1/z1 + 1/z2 + 1/z3

                                                                                    1/z =1/50 +1/50 +1/50

                                                                                          =0.06

                                                                                       Z =16.67%

% impedance at 11 KV bus                                              =8.8927% +16.67%

                                                                                          =25.56%

Fault MVA at 11KV bus =(base MVA ×100)/(total %impedance upto11KV bus)

                                                                                         = (100×100)/25.56

                                                                                         =391.38

                                                                                         =400MVA

Fault current at 11KV bus                                               = (400×10⁶)/ (Г3×11×10³)

                                                                                         =20.99KA

                                                                                         ≈21KA

4.5 DESIGN OF CABLES AND OVER HEAD LINES

1)      FOR  110KV

Rated current at 110KV side                               = (60MVA)/(Г3×110KV)

                                                                             = (60×10⁶)/(Г3×110×10³)

                                                                             =314.91A

                                                                             =315A

Conductor size                                                     = (rated current)/(current density)

Here we are taking cu conductor

The current density of cu                                    =1.2A/mm²

Size of conductor                                                =315/1.2    =262 sq.mm

So we are taking 300 sq.mm conductor.

Checking the size of conductor whether it withstands the fault current

Area of the conductor                                         = 11.1×Гt ×fault current in KA

                                                                            =11.1×Г3×5.9

                                                                            =123.47 mm²

2)      FOR  11KV

Rated current at 11KV side                                = (20MVA)/ (Г3×11KV)

                                                                           = (60×10⁶)/ (Г3×11×10³)

                                                                           =1049.72A

                                                                             =1050A

Conductor size =(rated current)/(current density)

Here we are taking Al conductor

Size of conductor                                                =1050/0.8 =1312.5sq.mm

So we are taking 4 runs of 400 sq.mm 3core XLPE cable from the secondary of transformer to the 11KV distribution pane l. for the 11KV distribution panel the busbar size is runs of 100mmX10mm CU conductor

4.6 SELECTION OF CIRCUIT BREAKER

A)    110 KV

Rated current                                                                   =315A

Taking factor of safety                                                    =4

CB rating                                                                         =252x4

                                                                                         =1260A

Available rating in the market                                         =1250A

Rating of CB                                                                   =1250A

Short circuit current at 110KV side                                =5.9 KA

                                                                                        =6KA

Considering future expansion, CB’s are selected such that rated normal current is 1250A and rated short circuit current breaking current 25KA.

B) 11KV

Rated current                                                                    =1050A

Taking factor of safety                                                     =2

CB rating                                                                          =1050X2

                                                                                          =2100A

Available rating in the market                                          =2500A

Rating of CB                                                                    =2500A

Short circuit current at 11KV side                                   =21 KA

Considering future expansion, CB’s are selected such that rated normal current is 2500A and rated short circuit current breaking current 50 KA.

4.7 SELECTION OF CURRENT TRANSFORMER

a)      110 KV

Rated current                                                           =315A

Available rating is the market                                 =500A

For metering and protection we are providing 4 no’s of secondary coils of 1A

Core utilization	Core1	Core2	Core3	Core4
	Main protection	Back-up protection	Metering	Different protection
burden	-		30VA
Minimum knee point voltage	600V			600V

b)     11KV

Rated current =1050A

Available rating in the market =1200A

For metering and protection we are providing 3 no’s of secondary coils of 1A

4.8 SELECTION OF POTENTIAL TRANSFORMER

A)    110KV

1.      Rated voltage           -110 ±10%

2.      Rated voltage KV (rms) -123

3.      Rated frequency -50 Hz

4.      System neutral earthing –effectively earthed

5.      Installation –outdoor

6.      Rated short circuit current KA -25

7.      Rated insulation level

a)      Impulse withstand voltage KV(peak) -450

b)      1 minute power frequency withstand voltage KV (rms) -185

8.      Number of secondary windings  -two

9.      Transformer ratio – 110/Г3KV/110/Г3,110/Г3 V

B)    11KV

1.       Rated voltage           -110 ±10%

2.      Rated voltage kv (rms) -123

3.      Rated frequency -50 Hz

4.      System neutral earthing –effectively earthed

5.      Installation –outdoor

6.      Rated short circuit current KA -25

7.      Rated insulation level

       a) Impulse withstand voltage KV (peak) -75

       b) 1 minute power frequency withstand voltage KV (rms) -38

8.      Number of secondary windings  -two

9.      Transformer ratio – 11000/Г3V/110/Г3V,110/Г3 V

4.9 ISOLATORS

TECHNICAL PARTICULARS

1.      Rated voltage KV(rms) -123

2.      Rated frequency Hz -50Hz

3.      System of neutral earthing –effective earthed

4.      Type of disconnect –horizontal break (double)

5.      Number of poles -3

6.      Installation –indoor

7.      Rated normal current amps -1000

8.      Rated short time withstand KA current -25

9.      Rated duration of short circuit =1sec

10.  Rated peak withstand current KA(peak) -62.5

11.  Operating mechanism –manual/motorized –automatic

11KV distribution feeder, current transformer, circuit breaker, cable

4.10 CT’S FOR 11KV FEEDERS

Rated secondary current -1049.72A

=1050A

Four feeders are taken from one transformer.

So current through one feeder =1050/4 =262.5A

                                                               = 263 A

Available rating for ct in the market is 300A

For metering and protection we are providing 3 secondary coils

Rating of CT =300/1-1-1 A

4.11 CB’S FOR 11KV FEEDERS

Rated normal current =263 A

In each feeder

Taking factor of safety =4

CB rating =263×4 =1052A

Available rating in the market =1250A

Short circuit current at 11KV =21KA

Considering future expansion CB’s are selected such that rated normal current is 1250 A

And rated short circuit breaking current is 50KA.

4.12 CABLE FOR 11 KV FEEDERS

Rated normal current =263 A

In each feeder

Size of conductor = (rated normal current)/(current density)                 

Considering economical aspects we are taking Al as the conductor.

 Size of Q conductor =263/0.8 = 328.75 sq.mm

Available size of conductor is the market is 400sqmm 3 core 11KV XPLE cable

4.13 DESIGNING OF EARTH MAT

                           40m

                                                            40 m

4.13.1 TO CALCULATE THE SIZE OF EARTH CONDUCTOR

For copper brased joints the formula for area of conductor A = 0.044×i×Гt

A= 0.0044×21000×Г3

A= 160.042 mm sq

Taking 20% allowance are given to the cross sectional area for a corrosive environment

i.e. A =192.05 mm sq

So we provide 35X 6 mm sq CU for earth mat which posses an area  of 210 mm sq. hence we propose 35X 6 mm sq CU strips to be buried at 0.5 m below the ground .

Assuming earthmat for a spacing of 2m, total no; of line =42

Resistivity, ρ =132Ωm

Spacing, D =2m

N= 42

H=0.5m

L=total length of conductor = (40X42) =1680m

Area =40X40 =1600m sq

Grid resistance Rg =ρ/ (4Xr) + ρ/L   -------------(1)

Assuming the earthmat to be a circle, A =1600m,sq

∏r² =1600m.sq

R =22.57 m

Substituting the value in eqn (1)

Rg =132/(4X22.57)+132/(16800 =1.54Ω

Inorder to reduce the resistance below 0.5Ω we provide a chemical named Bromite in the soil.

*    *    *    *    *

CHAPTER 5

COST ANALYSIS

5.1 COST ANALYSIS FOR GIS EQUIPMENTS

Sl.No.	Particulars	Quantity	Unit	Rate per unit	Amount in crores
	GIS EQUIPMENT
1.	1feeder +1transformer+1bus coupler	2	Set	5Crore	10
2.	1transformer section	1	Nos.	2crore	2
3.	Metering section &earthing switch	1	Nos.	4crore	4
4.	110KV,20MVA transformer	3	Nos.	51,00,000	1.5
5.	Transformer control &relay panel	2	Set	600000	0.12
6.	11KV distribution panel with 12 feeders &3bus coupler with relays &metering	1	Set	50,00,000	0.5
7.	Station battery				0.015
8.	Rectifier arrangement				0.005
9.	300mm2110KV straight joint	06	Nos.	15000	0.009
10.	415V LT panel for substation	01	Nos.	2,00,000	0.02
11.	Earthing material copper 50*6 sq mm Including all equipment earthing	10	Tonnes	500000/ton	0.5
12.	11kv ,3C *300Sqmm cable (11KV distribution panel to RMU)	300	Metre	5000/m	0.15
13.	RMU	12	Nos.	5,50,000	0.66
14.	3core*400sq mm  110KVXLPE cable (transformer to 11kv distribution panel )	120	Metre	30000/m	0.36
15.	Auxiliary transformer 200KVA outdoor oil cooled	1	Nos.	1,60,000	0.016
16.	1C*300sq mm 110KV X LPE cable /copper conductor with adequate insulation angle iron trace supports, brackets	60	Metre	5000.00	0.03
17.	Cable glands, cable crimping sockets etc	Lumpsum			0.03

 Labour charges @ 10% =1.94 crore

Contingency charges @ 10% =1.94 crore

Transportation charges @ 55 =0.97 crore

Cost for GIS equipment =24.25 crore

5.2 COST ANALYSIS OF FEEDER BAY- KAVANAD

SL.NO	Particulars	Quantity	Unit	Rate per unit	Amount in crores
1.	110kv lighting arrester	6	Nos.	42,000	0.025
2.	110kvsf6 circuit breaker	1		4,50,000	0.045
3.	110kvbus isolator	3	Nos.	61,000	0.018
4.	110kvline isolator	6	Nos.	72,000	0.0432
5.	110kv CT	3	Nos.	71,000	0.0213
6.	110kv  PT	3	Nos.	72,000	0.0216
7.	Feeder control/ relay panel			4,00,000	0.04
8.	Control cable	Lumpsum		3,50,000	0.035
9.	300mm2 XLPE 3 core UG cable	7.2	Km	8,13,000/km	0.5853
10.	300mm2 ACSR conductor for bus extension and for feeder bay	60		15000.00	0.09crore
11.	Supporting angle iron for line erection	20		20,000/tonne	0.04
12.	Suspension isolator’s suitable for 110KV	3		30,000/set	0.009
13.	Cable trench cable laying	Lumpsum		2,00,000.00	0.02
14.	110KV ,300sq mm straight jointing kit	3	Nos.	15,000	0.045
15.	PLCC cable for carrier communication	7.2	Km	50,000.00/km	0.036
16.	Cable duct	7.2	Km	2,50,000.00/km	0.18
17.	Angle iron support on the cable duct	2	Tonne	20000/ton	0.004
18.	Earthing material GI strips	3	Tonne	200000	0.06
19.	Nuts, bolts, washers etc	Lumpsum		25,000	0.0025
Total     = 1.2809 crores Labour charges                                @ 10%              =1.94 crore Contingency charges                      @ 10%              =1.94 crore Transportation charges                  @ 5%                 =0.97 crore Cost for  constructing feeder in Kavanadu S/S =1.601 crore 5.3 COST ANALYSIS (FEEDER SUPPLY )  ---AYATHIL  S/S
SL.NO	Particulars                                       Quantity             Unit         Rate per unit     Amount in crores
1.	110kv lighting arrester	6	Nos.
2.	110kvsf6 circuit breaker	1
3.	110kvbus isolator	3	Nos.
4.	110kvline isolator	6	Nos.
5.	110kv CT	3	Nos.
6.	110kv  PT	3	Nos.
7.	Feeder control/ relay panel
8.	Control cable	Lumpsum
9.	300mm2 XLPE 3 core UG cable	7.2	Km
10.	300mm2 ACSR conductor for bus extension and for feeder bay	60
11.	Supporting angle iron for line erection	20
12.	Suspension isolator’s suitable for 110KV	3
13.	Cable trench cable laying	Lumpsum
14.	110KV ,300sq mm straight jointing kit	3	Nos.
15.	PLCC cable for carrier communication	7.2	Km	15,000
16.	Cable duct	7.2	Km	2,50,000.00/km
17.	Angle iron support on the cable duct	2	Tonne	20000/ton
18.	Earthing material GI strips	3	Tonne	200000
19.	Nuts,bolts,washers etc	Lumpsum		25,000

5.4 COST ANALYSIS OF GIS BUILDING

SL.NO	DESCRIPTION	quantity	unit	Rate per unit	Amount in crores
1.	Building construction cost of three storied RCC building (30m*26m*12M)	2340	Sq.mm	2100.00	0.4914
2.	M>S structure for cranes supporting frames for equipments	4000	Kg	60.00	0.024
3.	Motorized crane (20 ton capacity)	1	no	8,00,000.00	0.08
4.	Electrification of the building	LS		2,50,000.00	0.02
5.	Sanitation &plumping	LS		1,50,000.00	0.015
6.	Demolishing of existing quarters	LS		50,000.00	0.005
7.	Developing of substation yard	LS		1,00,000.00	0.01

Total  =0.6454 crore

5.5 TOTAL COST FOR ENTIRE PROJECT

COST ANALYSIS =GIS EQUIPMENTS AND OUTGOING FEEDERS =24.25 crore

COST ANALYSI S (FEEDER SUPPLY)- KAVANAD S/S =1.601 Crore

COST ANALYSIS (FEEDER SUPPLY) -AYATHIL S/S =1.02 Crore

COST ANALYSIS OF GIS BUILDING =0.6454 crore

GRAND TOTAL=27.52 Crores

CHAPTER 6

ADVANCED CONTROL SYSTEM

6.1 INTRODUCTION

           An advanced control system is being proposed for the 110KV substation. In this advanced control system, whole of the substation components are modeled using simulink in MATLAB software. MATLAB is a software introduced by a company known as ‘Math Works. Inc.” which is used for mathematical operations. This software is basically a modeling software and any equipment can be modeled using this software.  Then the model is simulated by pressing “ Start Simulation” button. Afterwards we can view the characteristics at any part of the system by viewing the scope. Basically three main equipments are needed to interface the incoming busbar voltage with the computer. The three main equipments are-

·         Voltage Transducer

·         Microcontroller

·         Parallel Port Programmer

        The incoming busbar voltage is fed to the voltage transducer. Since the output of the voltage tansducer is analog in nature and the input to the microcontroller must be digital in nature, an Analog to Digital converter must be placed in between the voltage transducer and microcontroller to interface them. The output of the microcontroller is fed to the parallel port programmer. The last stage includes the connection of parallel port programmer and computer.

6.2 VOLTAGE TRANSDUCER

        Voltage Transducer measures AC Voltage and converts it to an industry standard output signal which is directly proportional to the measured input. These Transducers provide an output which is load independent and isolated from the input. The output can be connected to Controllers, Data-Loggers, PLC's, Analog / Digital Indicators, Recorders for display, analysis or control. They are ideal for SCADA, Energy Management, Telemetering for Remote, Local as well as Central Monitoring Systems.

                   

                     VMT, VMT – TRMS                                              BPVMT, BPVMT – TRMS

6.3 MICROCONTROLLER

      A microcontroller (also microcomputer, MCU or µC) is a small computer on a single integrated circuit consisting internally of a relatively simple CPU, clock, timers, I/O ports, and memory. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for small or dedicated applications. Thus, in contrast to the microprocessors used in personal computers and other high-performance or general purpose applications, simplicity is emphasized. Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4 kHz, as this is adequate for many typical applications, enabling low power consumption (milliwatts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.

       Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, and toys. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.

 6.3.1 DETAILS OF ATMEGA 32

FEATURES

• High-performance, Low-power AVR® 8-bit Microcontroller

• Advanced RISC Architecture

– 131 Powerful Instructions – Most Single-clock Cycle Execution

– 32 x 8 General Purpose Working Registers

– Fully Static Operation

– Up to 16 MIPS Throughput at 16 MHz

– On-chip 2-cycle Multiplier

• Nonvolatile Program and Data Memories

– 32K Bytes of In-System Self-Programmable Flash

   Endurance: 10,000 Write/Erase Cycles

– Optional Boot Code Section with Independent Lock Bits

   In-System Programming by On-chip Boot Program

   True Read-While-Write Operation

– 1024 Bytes EEPROM

   Endurance: 100,000 Write/Erase Cycles

– 2K Byte Internal SRAM

– Programming Lock for Software Security

• JTAG (IEEE std. 1149.1 Compliant) Interface

– Boundary-scan Capabilities According to the JTAG Standard

– Extensive On-chip Debug Support

– Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface

• Peripheral Features

– Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes

– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture Mode

– Real Time Counter with Separate Oscillator

– Four PWM Channels

– 8-channel, 10-bit ADC

   8 Single-ended Channels

   7 Differential Channels in TQFP Package Only

   2 Differential Channels with Programmable Gain at 1x, 10x, or 200x

– Byte-oriented Two-wire Serial Interface

– Programmable Serial USART

– Master/Slave SPI Serial Interface

– Programmable Watchdog Timer with Separate On-chip Oscillator

– On-chip Analog Comparator

• Special Microcontroller Features

– Power-on Reset and Programmable Brown-out Detection

– Internal Calibrated RC Oscillator

– External and Internal Interrupt Sources

– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby

   and Extended Standby

• I/O and Packages

– 32 Programmable I/O Lines

– 40-pin PDIP, 44-lead TQFP, and 44-pad MLF

• Operating Voltages

– 2.7 - 5.5V for ATmega32L

– 4.5 - 5.5V for ATmega32

• Speed Grades

– 0 - 8 MHz for ATmega32L

– 0 - 16 MHz for ATmega32

• Power Consumption at 1 MHz, 3V, 25°C for ATmega32L

– Active: 1.1 mA

– Idle Mode: 0.35 mA

– Power-down Mode: < 1 μA

6.3.2 OVERVIEW

       The ATmega32 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega32 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.

        The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.

        The ATmega32 provides the following features: 32K bytes of In-System Programmable Flash Program memory with Read-While-Write capabilities, 1024 bytes EEPROM, 2K byte SRAM, 32 general purpose I/O lines, 32 general purpose working registers, a JTAG interface for Boundary-scan, On-chip Debugging support and programming, three flexible Timer/Counters with compare modes, Internal and External Interrupts, a serial programmable USART, a byte oriented Two-wire Serial Interface, an 8-channel, 10-bit ADC with optional differential input stage with programmable gain (TQFP package only), a programmable Watchdog Timer with Internal Oscillator, an SPI serial port, and six software selectable power saving modes.

       The Idle mode stops the CPU while allowing the USART, Two-wire interface, A/D Converter, SRAM, Timer/Counters, SPI port, and interrupt system to continue functioning. The Power-down mode saves the register contents but freezes the Oscillator, disabling all other chip functions until the next External Interrupt or Hardware Reset. In Power-save mode, the Asynchronous Timer continues to run, allowing the user to maintain a timer base while the rest of the device is sleeping. The ADC Noise Reduction mode stops the CPU and all I/O modules except Asynchronous Timer and ADC, to minimize switching noise during ADC conversions. In Standby mode, the crystal/resonator Oscillator is running while the rest of the device is sleeping. This allows very fast start-up combined with low-power consumption. In Extended Standby mode, both the main Oscillator and the Asynchronous Timer continue to run.

      The device is manufactured using Atmel’s high density nonvolatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serial interface, by a conventional nonvolatile memory programmer, or by an On-chip Boot program running on the AVR core. The boot program can use any interface to download the application program in the Application Flash memory. Software in the Boot Flash section will continue to run while the Application Flash section is updated, providing true Read-While-Write operation. By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip, the Atmel ATmega32 is a powerful microcontroller that provides a highly-flexible and cost-effective solution to many embedded control applications.

      The ATmega32 AVR is supported with a full suite of program and system development tools including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits.

6.3.3 PIN DESCRIPTIONS

Pin Configurations

Figure 1. Pinouts of ATmega32

VCC-    Digital supply voltage.

GND-    Ground.

Port A (PA7..PA0)-    Port A serves as the analog inputs to the A/D Converter. Port A also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pins can provide internal pull-up resistors (selected for each bit). The Port A output buffers have symmetrical drive characteristics with both high sink and source capability. When pins PA0 to PA7 are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running.

Port B (PB7..PB0)-     Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port B also serves the functions of various special features of the ATmega32.

Port C (PC7..PC0)-     Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port C output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins PC5(TDI), PC3(TMS) and PC2(TCK) will be activated even if a reset occurs. The TD0 pin is tri-stated unless TAP states that shift out data are entered. Port C also serves the functions of the JTAG interface and other special features of theATmega32.

Port D (PD7..PD0)-    Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port D output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port D also serves the functions of various special features of the ATmega32.

RESET-     Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. The minimum pulse length is given in data table. Shorter pulses are not guaranteed to generate a reset.

XTAL1-    Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.

XTAL2-     Output from the inverting Oscillator amplifier.

AVCC-    AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter.

AREF-        AREF is the analog reference pin for the A/D Converter.

6.4 PARALLEL PORT PROGRAMMER

6.4.1 GENERAL TYPES OF DIGITAL DATA COMMUNICATION

1.      Parallel

2. Serial

Parallel

Parallel communication requires as much wires as the no. of bits in a word for its transmission. Word may be a combination of 4, 8, 16, 32 or 64 bits etc.

Serial

Serial communication usually requires a minimum of 2 wires for data transmission in one direction. One wire is for data and other is for ground.

Parallel port identification on IBM PC

 Usually ports are found on the rear of computer and are of  the following two types;

1)      Male ports - having pins coming out of port.

      2)   Female ports - having holes for pins.

Parallel port is generally a 25 pin female connector with which a printer is usually attached.

Grouping Of Parallel Port Pins

i.  Data port

ii. Status port

iii. Control port

Data port:

•         It includes pin 2 to pin 9 with pin names Data-0 to Data- 9

•         It is usually for data output according to old “standard parallel port” standard.

ii. Status Port

Status port is an input only port i.e. Data can’t be output on this port but it can only be read.

iii. Control port

Control port is a read / write port. For printer purposes it is write only port

                 

6.5 PARALLEL PORT PROGRAMMER FOR ATMEGA 16/32

     In-system programmer means we can design a programmer circuit using simple parallel port interfacing such that our controller can be directly burned with the program while in the designed system or circuit board.

Following pins of Atmega16 is used in programmer circuit-

Pin No.	Description
6	MOSI (SPI Bus Master Output/Slave Input
7	MISO (SPI Bus Master Input/Slave Output)
8	SCK (SPI Bus Serial Clock)
9	Reset
10	Vcc
11	Ground

Table-Atmega16 Pins

• SCK – Port B, Pin 7

SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB7.When the SPI is enabled as a Master; the data direction of this pin is controlled by DDB7. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB7 bit.

• MISO – Port B, Pin 6

MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master, this pin is configured as an input regardless of the setting of DDB6. When the SPI is enabled as a Slave, the data direction of this pin is controlled by DDB6. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB6 bit.

• MOSI – Port B, Pin 5

MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB5. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB5 bit.

• RESET-Pin 9

Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running.

• VCC -Pin 10

Digital supply voltage(+5V).

•GND-Pin-11         Ground.

Parallel Port-

Parallel Port interfacing is the simplest method of interfacing. Parallel Port’s are standardized under the IEEE 1284 standard first released in 1994. It has data transfer speed up to 1Mbytes/sec. Parallel port is basically the 25 pin Female connector (DB-25) in the back side of the computer (Printer Port). It has 17 input lines for input port and 12 pins for output port. Out of the 25 pins most pins are Ground and there is data register (8 bit), control register (4 bit) and status register (5 bit).

Fig-Pin diagram of Parallel Port

Following Pins are used in parallel port-

Pin No.	Description
7,8,9	Data pins
10	Status pin
19	Ground

Table- Parallel Port Pins

Interfacing -

In programmer circuit pins of parallel port which are above described has to interface with pins of ATmega16 microcontroller which are responsible for in-system programming. The parallel port can be interfaced directly with microcontroller. To avoid reverse current we can use Schottkey diodes as safety precaution for pc motherboard.

Following pins of Parallel Port and ATmega16 are to be interfaced-

Parallel Port	Atmega16
Pin 7	Reset (Pin 9)
Pin 8	SCK (Pin8)
Pin 9	MOSI (Pin6)
Pin 10	MISO(Pin7)
Pin 19	Ground(Pin11)

Interface Connections-

Fig-Circuit Diagram of ATmega16 Programmer

Fig. The Snapshot

SOFTWARES USED:

WinAVR–  WinAVR is open source package in which we use two sub-programs

 Programmers, Notepad & Mfile.

Version-          2.0.8.718-basic

Creator-           Simon Steele

Purpose-          1. To write code.

                        2. To compile coding.

                        3. To generate Hex Code.

                        4. To burn Hex code.

6.6 MATLAB MODELS AND SCOPE OUTPUT

   As a demo for our proposal, we are including the MATLAB models and scope outputs of three relays namely-

·         Instantaneous relay

·         Differential relay

·         Overcurrent relay

INSTANTANEOUS RELAY MODEL

SCOPE OUTPUT OF INSTANTANEOUS RELAY

DIFFERENTIAL RELAY MODEL

SCOPE OUTPUT OF DIFFERENTIAL RELAY

OVERCURRENT RELAY MODEL

SCOPE OUTPUT OF OVERCURRENT RELAY

*    *    *    *    *

CHAPTER 7

CONCLUSION

       From the review of conventional substation the large size & inadequacy in the safety factor was noted. Thus, the need of a compact and safe working environment came up. The properties of SF6 was studied and this lead to the design of a 110KV GIs substation for Kollam city with SF6 as an effective insulating medium. The cost analysis is also carried out. We have also proposed a advanced control system for the substation using MATLAB software which enables highly technical as well as easy monitoring of the operations occurring in the substation.

       Certain things to be taken care are that proper steps should be taken in the design and maintenance of the substation equipments, else it may affect the satisfactory functioning of the substation. Space savings, the most significant benefit of GIS substation should be evaluated not only in terms of locating the substation where it benefits the electrical system but also provides other financial oppurtunities or avoid controversy and delays.

REFERENCES

1.      LEEDS W.M.FRIEDDRICH R.E,WAGNER C.L.HT.CB  with Sf6(report of international conference about high voltage ,1960

2.      BROWN T.E, LEEDS W.M –A new extinction agent for breaking devices (report of international conference about HV,1960)

3.      MOHANA RAO.M, NAIDU M.S –very fast transient voltage and transient  enclosure voltage in a GIS  substation (ELECTRICAL INDIA,15^th April 1997)

4.      PHIL BOLIN –Engineers note book (ELECTRICAL WORLD March/April 2000)

5.      www.toshiba.com

6.      www.aba.com

7.      British Library Direct:  A technical design 110KV  GIS substation

8.      www.jacobsbabtie.com/