Generation GCO10-P4 - TT10 (Day4)

TOPICAUTOMATIC VOLTAGE REGULATORSYNCHRONIZING GRID VOLTAGE CONROLSWITCHYARD EQUIPMENT

COURSE OBJECTIVESAt the end of day4, participants will be able to:-Describe Automatic Voltage RegulatorDescribe Excitation SystemDescribe MVAR and System Voltage relationship in an electrical IslandDescribe System Voltage ControlExplain Synchronizing Generator Describe Switchyard Equipment

COURSE CONTENTAutomatic Voltage Regulator

Synchronizing a Generator

Grid System Voltage Control

Switchyard Equipment and Operating Protocol

GENERATOR AUTOMATIC VOLTAGE REGULATORWhy do we need AVR for Generator ?Electric power is delivered throughout the Grid system at regulated voltage. Large voltage fluctuation could cause damage to connected electrical equipment. System voltage can be maintained by regulating terminal voltages of a generators.

GENERATOR AUTOMATIC VOLTAGE REGULATORWhy do we need AVR for Generator ?

AVR regulates generator terminal voltages by controlling direct current to the field winding at a relatively low voltage (50-500 volts) compare to the generator stator voltage.

This is normally known as generator excitation system.

Potential Source Excitation System Block DiagramPTGENERATORPOWER RECTIFIER / SCRDCREG.ACREGULATORCTPOWERPOTENTIALTRANSFORMER(PPT)

Generator Excitation EquipmentThe excitation equipment is composed of :- - power potential transformer- power rectifier - ac regulator- dc regulator - other optional equipments

Power potential transformer provides the power source for the excitation

Power rectifier provides the dc excitation current to the generator rotor coil

Generator Excitation EquipmentThe regulator circuitry consists of two basic regulators:-

ac regulator - controls generator terminal voltagedc regulator - controls generator field voltage

The dc regulator loop is active in the ac regulator mode, operating as an inner control loop to the outer regulator loop.

Potential Source Excitation System Block DiagramPTGENERATORPOWER RECTIFIER / SCRDCREG.ACREGULATORCTPOWERPOTENTIALTRANSFORMER(PPT)

Voltage Control Cause of Voltage Deviation

Effect of Voltage Deviation

Use of Voltage Control Equipments

Role of System Operator

Causes of Low Voltage High power transfer

Sudden loss of transmission line

Loss of Mvar sources

Failure to get ahead of the voltage

Sudden increase of large loads

Causes of High Voltage Low power transfer

Loss of transformer

Loss of load

Effects of Low Voltage Customer equipment

Power losses

System equipment

Load magnitude

Angle stability

Effects of High Voltage Over-excitation in transformers

Load magnitude

Angle stability

Power losses

Customer equipment

Use of voltage control equipments Capacitor

Reactor

Transformer tap changer

Generator

Synchronous condenser

Static Var compensator SVC

Four Reasons to Keep Voltage High Increase power transfer

Minimize losses

Increase Stability (reduce power angle)

Increase reactive output

Role of System Operator Monitor voltage

Take actions to raise voltage

Take actions to lower voltage

Maintain reactive reserves

SYNCHRONIZINGThe following notes will explain :- The importance of synchronizing Conditions that must be met in order to synchronize Synchronize two generators together Synchronize a generator to the grid or infinite bus

SYNCHRONIZINGFive conditions must be met for two generators to be synchronized :-The number of phases must be the same.The direction of rotation must be the same.The frequencies must be closely matched.The voltage amplitudes must be closely matched.The phase angles must be closely matched.

SYNCHRONIZINGNUMBER OF PHASESThe number of phases in the generator must equal the number of phases of the bus it is synchronizing to.This should only be a consideration when initially installing a generator.

SYNCHRONIZINGDIRECTION OF ROTATIONThe electrical rotation of the generator being brought on line must match the electrical rotation of the bus it is synchronizing to.GeneratorBUSThis should only be a consideration when initially installing a generator.

SYNCHRONIZINGVOLTAGE AMPLITUDESVoltage amplitudes of the unit coming on line should be slightly higher than the bus voltage so that the unit will be feeding out power when it ties on.GeneratorBUSThe voltage amplitude can be adjusted at the voltage regulator (Raise / Lower).Voltage AmplitudeVoltage Amplitude

SYNCHRONIZINGFREQUENCY MATCHThe frequencies of the on coming unit and bus must be matched. In some cases, the on-coming unit may have a slightly faster frequency in order for the oncoming generator to immediately start producing power.GeneratorBUSThis is where we get the phrase slow in the fast direction.

SYNCHRONIZINGPHASE ANGLE MATCHThe phase angle of the generator and bus must be matched.In this example the generator and bus have the same frequency but are out of phase. They will be in phase when the two wave forms over lap each other.BUS

SYNCHRONIZINGPHASE ANGLE MATCHAt the point the two wave forms overlap each other the synchroscope should be pointing at 12 oclock and the phashing lights should be dark.GeneratorBUSThe phasing lights should be dark because they are typically powered from the voltage potential that exists when the two wave forms are out of phase from each other.

SYNCHRONIZINGWHY IS SYNCHRONIZING IMPORTANT ?Proper synchronizing of generators is required not only to prevent catastrophic failure of components but also to prevent accelerated wear of switch gear components caused by closing the breaker when even a small voltage potential exists between units.GeneratorBUSPrevent failure of Generator, Switchgear (Circuit Breaker), Transformer, Auxiliary Equipmentsetc.

24 26 APR 2006SWITCHYARD EQUIPMENTObjective Provide System Overview of a Switchyard Equipment for Thermal Power Plant Describe the Major Components in Switchyard Discuss the Operations and Control aspects Example : Perai Power Station

SWITCHYARD OVERVIEWBasic Function The function of a Station Switchyard is mainly to distribute generated power to the power system network (or grid).

And when necessary, to supply power back from the GRID to the plant startup transformer (or station transformer)

SWITCHYARD OVERVIEWBasic Description

As shown in Figure 1.A, refers to a typical system having :- generation at 11 kV transmission at 132 kV with the major auxiliaries being supplied at 3.3 kV

SWITCHYARD OVERVIEWBasic Description The importance of the Switchyard as a vital link inthe generation, transmission and utilisation ofelectric power can be seen by reference to the blockdiagram of a typical system In the example show, the power generated by thegenerators at 11 kV, is stepped-up by thegenerator transformers to 132 kV and supplied tothe busbars through a 132 kV circuit breaker

Basic Description

From the busbars the power is distributed, via other circuit breakers to :1. Outgoing Transmission Lines (or Feeders) :2. Station Transformers to supply in-house electrical needs : and3. Local Transformers to supply the local consumers.SWITCHYARD OVERVIEW

SWITCHYARD OVERVIEWBasic Description The station transformers and local transformers areof the step-down variety The station transformers step-down/reduce the busbarvoltage from 132 kV to 3.3 kV use by the stationauxiliaries such as pumps and fans, as well as lightingand other needs of the power station. The local transformers step-down the busbar voltage to33/11 kV and supplies power to the 33/11 kV switchboard, from where it is distributed to local industrial consumers and local distribution substations.

Basic Description From the busbars the power is transmitted to the transmission lines at HV, in order to reduce line-losses At the remote end of the transmission lines are main intake substations where the voltage is stepped-down to11 kV and distributed by HV underground cables tovarious distribution substations From there, it is further stepped-down to 415V to supplythe LV overhead mains, and finally reaches theconsumersSWITCHYARD OVERVIEW

Basic Description The 132 kV Busbar System supplied by 120MW Units, via their respective generator transformer (G/T) 132/3.3kv Station Transformers are fed from the 132 kVbusbars Five feeders at 132 kV also connected to the 132 kVbusbars 132/33 kV Interbus Transformers connecting the 132busbars to the 33 kV busbarsSWITCHYARD OVERVIEW

Major components in a Switchyard1.Busbars2.Transformers3.High-Voltage Circuit Breakers4.Isolators5.Earthing (Switches, Transformers, Resistances)6.Surge Diverters7.Line Traps and8.InsulatorsSWITCHYARD OVERVIEW

132 kV Busbar System

The function of the 132 kV Busbar System is toreceive power from the generators via theirrespective step-up generator transformers and circuitbreakers and distribute it to the 132 kV feeders

Some power is also channelled to the 33 kV busbarsvia the Interbus TransformersSWITCHYARD OVERVIEW

Some basic busbar description An electric busbar is defined as any system of conductors to which three or more electric circuitsare connected The word busbar is taken from Latin wordomnibus which means for all (shortened tobus - a vehicle forcarrying everyone) Thus the term busbar means a set of conductors orbars (at first only solid bars were used - voltagebeing low), to which all the incoming and theoutgoing electrical circuits are connectedSWITCHYARD OVERVIEW

Some basic busbar description Since busbars are just a set of conductors they can even take the form of overhead wires strungbetween poles using insulators This type of construction is called a Flexible Busand is used for very small stations with one or twomachines and a couple of feeders; because it is verycost-effective But when many circuits are involve, there may beproblems of clearances due to sag and sway of the wires during stormsSWITCHYARD OVERVIEW

Some basic busbar description For most large power station and main-intake substations the Rigid Bus system is used because ofits stability and convenience of connection to severalelectrical circuits

The rigid busbars are made of tubular copper alloyand mounted solidly on free-standing verticalporcelain insulators

(The two simple busbar systems mentioned above isshown in the pictures)SWITCHYARD OVERVIEW

132 kV Busbar System The 132 kV busbar system normally has two sets of busbars, the Main and the Reserve busbars The Main busbar has a row of three parallel horizontalbusbars, one for each phase; and surrounding this rowon three sides is the Reserve busbar (also with threeparallel bars for R, Y, and B phases) This formation is used to enable easy connection to thevarious incoming and outgoing circuit breakers, whichwould be almost impossible otherwise, because of thenumerous crossings of conductors involvedSWITCHYARD OVERVIEW

132 kV Busbar System

The 132 kV busbars are supplied by Generator setsthrough their respective Generator-Transformers which step-up the generated voltage to 132 kV Outgoing feeder circuits Distribution transformers Station transformers Circuit breakers, isolators and earthing switches.SWITCHYARD OVERVIEW

132 kV Busbar System Each incoming generator transformer circuit breakerand each outgoing Feeder CB is connectedDisconnect Switch (or Isolator) The isolator is used for isolating the circuit breaker from the system , for maintenance purpose, and isonly to be operated when the CB is OFFSWITCHYARD OVERVIEW

132 kV Busbar System In addition , each outgoing Feeder CB line Isolatorhas an Earthing Switch fitted This switch is closed only after the Line Isolator isopened, and the line is dead, to protectmaintenance personnel working on the yard / lines. The local transformers ground point however, are permanently earthed through an earth resistanceSWITCHYARD OVERVIEW

132 kV Busbar System A Bus-Coupler (which is a circuit breaker) is also provided to connect the Main busbar to the Reservebusbar This bus-coupler must be closed before any transfer ofplant is carried out between the Main and Reserve bars The 132 kV busbars have separate protection systems installed for Main and Reserve busbars Whenever a fault occurs within the protected zone, all theCBs on that busbar will trip out and thus clear that busbarSWITCHYARD OVERVIEW

132 kV Busbar System - Operation In normal operation, both Main and Reserve bars arein service, with the Bus-Coupler closed If it is necessary to isolate either of the busbars, thenall the machines and the feeders have to betransferred to one busbar, after which the bus-coupler is openedSWITCHYARD OVERVIEW

132 kV Busbar System - Operation When the Bus-Coupler connects the two Main andReserve bars, the synchroscope must be used sinceparalleling of two power sources is involved If both bars are energised, the synchroscope pointerwill be stationary at 12 o-clock position and bothrunning and incoming readings will be the sameSWITCHYARD OVERVIEW

132 kV Busbar System - Operation With the bus-coupler and its Isolators closed, on-load busbar transfer is permitted on all circuits; since withthe bus-coupler closed, both the Main and ReserveBars are at the same voltage Operation of the isolators are allowed after the respective Breaker is opened This is not the same as using the isolators to break ormake load current which, is forbiddenSWITCHYARD OVERVIEW

132 kV Circuit Breakers The function of a HV CB is to interrupt a circuitunder load conditions In addition to breaking the normal load current, itcan also interrupt an overload or fault current severaltimes greater than normal current under short circuit conditionsSWITCHYARD OVERVIEW

132 kV Circuit Breakers A CB interrupts circuit by opening its contacts and theninterrupting the current by extinguishing the resultant as rapidly as possible This is created by the current trying to bridge the gapas the contacts first separate The air between the arc becomes very hot and ionizes, thusacting as a conductor The arc is extinguished by increasing the distance betweenthe contacts as rapidly as possible and providing somemeans of force-cooling the arc. Such as by creating astrong flow of oil and gas along its entire pathSWITCHYARD OVERVIEW

132 kV Circuit BreakersBasic CB priciples - are interruption When the current is interrupted, the field collapses andsince energy cannot be destroyed, the energy in themagnetic field is converted back into electric energy. The faster the current goes to zero, the higher thevoltage induced Thus an arc allows the current to flow for a few cyclesmore, to enable the magnetic fields to decay graduallywithout excessive over voltages The design of a CB is meant to minimize this arc. Toextinguish it fast and prevent it from restrikingSWITCHYARD OVERVIEW

132 kV Busbar Coupler The function of a bus-coupler is to connect the Mainand Reserve busbars, thus allowing for the transferof circuits from on bus to the other This can be partial transfer, so as to share out theload and generator outputs, or total transfer tocompletely change over all the circuits to one busbar(for maintenance) If the bus-coupler is open, an interlock preventoperation of any of the isolatorsSWITCHYARD OVERVIEW

132kV Busbar Coupler

The bus-coupler is a 132 kV circuit breaker

To operate, the synchroscope must be used sinceparalleling of two power sources is involvedSWITCHYARD OVERVIEW

132 kV Isolators isolators (or Disconnect Switches) are primarily usedfor Off-Load switching only; to isolate, connect, orchange the alignment of electrical equipment such asbusbars, breakers, feeders and transformers They are not to be used for on-load switchingbecause they do not incorporate any arcextinguishing devices, and opening or closing underload will cause the contacts to melt therebydestroying the isolatorsSWITCHYARD OVERVIEW

132 kV Isolators - Operations The 132 kV isolators can only be operated locally, since motor operation is not provided Since isolators are to be used for non-load currentbreaking only, it is essential to verify that theassociated 132 kV CB is off before trying to operatethe isolator To CLOSE the isolator, first ensure that all PTWs(permits-to-work) have been cancelled and that theplant is ready for operationSWITCHYARD OVERVIEW

Earthing Switches These 3-pole earthing switches are fitted to line isolators Their function is to earth the feeder line after theisolator is opened, if maintenance is to be carried outon the plant side of the isolator Earthing the line after it has been isolated, protectsmaintenance personnel from inadvertent energisingof the line from the other end, since this willimmediately trip off the supply circuit breaker onearth faultSWITCHYARD OVERVIEW

Equipment Earthing And System Earthing equipment earthing purely for the protection of the user In this case the exposed, non-current carrying metal parts of a piece of electrical equipment, say a table-lamp, is connected electrically to earth or ground If there is an internal short-circuit. (say the live wireinsulation is broken) the body of the lamp becomes aliveand would pose a grave danger to anyone who touches it But if the body of the lamp is earthed, the current would take the line of least resistance and find an easy path tothe ground, thus protecting anyone who touches the lampfrom electric shockSWITCHYARD OVERVIEW

Equipemnt Earthing And System Earthing system earthing is the intentional shorting of some point in the electrical system (usually theNeutral point of transformers) to earth (orground), in order to provide circuit stability andprotectionSWITCHYARD OVERVIEW

Equipment Earthing And System Earthing In a three-phase system, earthing the neutral or star-point of a distribution transformer does the following :1.Maintains phase voltages at the correct level2.Provides a safe path for fault current to ground3.Enables protective relays to be used for earth-fault4.If an earthing resistance is used, enables fault current restriction5.With the used of are-suppression coil, enables parts of thesystem to remain in service even with say, a fault on onephase, and6.On L.V. overhead lines provides single phase supply dodomestic consumersSWITCHYARD OVERVIEW

Earthing Switches - Operation Prior to operating the earthing switch it is vitally important to ensure that the associated isolator is open and the line isdead Although an interlock is provided it may have been defeated, hence the necessity for extreme care The operation itself is simple; merely lifting the operatinghandle and if it is free, rotate it in a smooth movement tothe closed or open position as necessary When closed ensure that the contacts have made firmly, andthat they are not merely half closed When open also visually check to verify that the contractsare properly parted and not jammedSWITCHYARD OVERVIEW

Surge Diverters (Lightning Arresters) Surge Diverters protect the plant and transmissionlines against abnormal over voltages during switchingsurges and especially during lightning strikes on thesystem Basically surge diverters act as insulators at normal rated voltages, but become conductors at extremelyhigh voltages to carry away the surge currents safely toearth As soon as the voltage comes back to normal the diverter once more reverts to acting as an insulatorSWITCHYARD OVERVIEW

Surge Diverters - Operations A surge diverter operates on the principle that undernormal or rated voltage conditions the diverter actsas an insulator and prevents any current flow throughit When an over voltage occurs, the non-linearresistance material within the diverter acts as a lowimpedance conductor and diverts the surge currentsafely to earthSWITCHYARD OVERVIEW

Surge Diverters - Operations The normal 50 Hz current is prevented from followingthrough to ground by the inherent resistance of the arrester The arc is quickly extinguished and its energy dissipated,all within a fraction of a millisecond, and the arrester isready to protect against the next voltage surge surge diverters, once installed and commissioned, operateon their own without any intervention by operators. Theonly task needed is routine recording of the counterreadingsSWITCHYARD OVERVIEW

Line Traps A Line Trap is part of the PLC (Power Line Carrier) system used to superimpose high frequency carrier signals over the power transmission lines

Refer PictureSWITCHYARD OVERVIEW

Line Traps There is no need for operator to intervene inutilizing Line Traps

Once tuned and commissioned it becomes a part ofthe fixed electrical equipment that needs no specialcontrol under normal running conditionsSWITCHYARD OVERVIEW

HV Current Transformers The function of a HV CT is primarily to enable the line current in a HV power circuit to be measured by meters and protection relays The current transformer achieves this in two ways1.By isolating instruments, relays and meters from high line voltages, where the delicate andprecise instruments cannot accommodate2.By transforming the line current to levels suitable for measurement on standard instruments, meters, and relaysSWITCHYARD OVERVIEW

HV Current Transformers A current transformer supplies the instrument or relay which is connected to its secondary windings,with a current proportional to the primary current,but small enough to be safe for the instrument orrelay The secondary of a CT is usually designed for a ratedcurrent of 5A or 1A The primary winding is connected in series with thelineSWITCHYARD OVERVIEW

HV Current Transformers There is no necessity for operator intervention in utilising Current Transformers Once properly commissioned and installed itbecomes a part of the fixed electrical equipment thatneeds no special control under normal runningconditions Routine checking only involves observing that theoil level, in the expansion tank on top of the CT,does not fall below the set markSWITCHYARD OVERVIEW

Voltage Transformers The function of a voltage transformer (VT) is similarto that of the step-down power transformer i.e. toreduce the high voltages on a circuit, to levels lowenough to be measured by voltmeters and protectiverelays The only difference being that the amount of powertransformed by a VT is very small in the order ofsay between 100 VA and 1500 VA only, ascompared with several hundred or thousands of kVAfor power transformersSWITCHYARD OVERVIEW

Voltage Transformers The VT or potential transformer (PT) is used to reduce highvoltage to a value that is low enough for use with voltmetersand relays The normal VT consists of a primary and a secondary winding wound about a laminated iron core as for a normalstep-down power transformer However for high voltages, a Capacitor Voltage Transformer (CVT) is preferred over the two-winding typeof VT Both types of VTs are normally installed, namely theconventional electro-magnetic ones (Type EMFC 145) andthe capacitor voltage transformers (Type CP)SWITCHYARD OVERVIEW

Voltage Transformers There is no necessary for operator intervention in utilisingCapacitor Voltage Transformers Once properly commissioned and installed it becomes apart of the fixed electrical equipment that needs no specialcontrol under normal running conditions Routine checking only involves inspection to confirm thatthere is no oil leak or accumulation of soot or dust on theporcelain The oil level should not fall below the marked level andtends to expose the paper insulation to the air, the unit mustbe taken out of serviceSWITCHYARD OVERVIEW

Neutral Earthing Resistance The Neutral Earthing Resistance is connected to theneutral point of the electrical system And its function is to limit the current flowing toearth during major faults (such as short circuit toearth) on the system This intentional shorting of same point in theelectrical system (usually the Neutral point oftransformers) to earth (ground), is to provide circuitprotectionSWITCHYARD OVERVIEW

Neutral Earthing Resistance In a 3-phase system, earthing the neutral or star-point of adistribution transformer does the following :1.Maintains phase voltages at the correct level2.Provides a safe path for fault current to ground3.Enables protective relays to be used for earth-fault4.If an earthing resistance is used, enables fault current restriction5.With the use of arc-suppression coils, enables parts of the system to remain in service even with say, a faulton one phase, and6.On L.V. overhead lines provides single phase supplyto domestic consumersSWITCHYARD OVERVIEW

Neutral Earthing Resistance Distribution systems which have low fault MVA levels can be grounded using a solidly earthedneutral For large power systems where high fault levels are grounded using a resistance-earthed neutral These resistances can be either of the metal earthingtype (either cast-grid or continuous strip) or theliquid earthing typeSWITCHYARD OVERVIEW

Neutral Earthing Resistance - Operations Once installed and commissioned the earthing resistance becomes a part of the fixed electricalequipment that needs no special control undernormal running conditions, except to occasionallyoperate the isolators to solidly earth eithertransformer when it is on maintenance Routine annual inspections are made to check forcrack or damage of insulators, for change of colourof resistors, for corrosion of panels etc.SWITCHYARD OVERVIEW

Interbus Transformers

The function of an Interbus Transformer is to connect two sets of busbars having different voltagessuch as the 33 kV Busbars and the 132 kV Busbars

So as to enable the system load to be shared bygenerators on both busbarsSWITCHYARD OVERVIEW

Interbus Transformers In some cases, an auto-transformer is used instead ofthe usual two-winding transformer, usually when theratio is small; for the following reasons;1.Since it is a single coil, it uses less materialand some insulation level2.The electrical losses is less and better voltageregulationSWITCHYARD OVERVIEW

132 kV Panels The 132 kV control panel in the ECR is vital to the remote operations and control of the major 132 kVequipment in the switchyard Visual indications of the status of each circuit breakerand isolator are given on the mimic board The operating parameters of each major 132 kVcomponent, such as voltage, current, power and reactivevolt-amperes are also indicated The various relays that operate during a fault are alsoindicated on the facia of the panelSWITCHYARD OVERVIEW

132 kV Panels Each equipment panel contains meters, switches, miniaturecircuit breakers, indication lights, alarms and synchronisingsockets, like ammeter, voltmeter, Megawatt meter and kVArmeter, ammeter phase-selection switch Facia relay indication panel, which shows thenumber and type of relay operated; with buttons toaccept, reset (orcancel) and for test an Auto-Reclose off/on switch and a Carrieroff/on switch indication lamps for CB Spring Charged and TripCoil Supervisory, with the hand-trip and auto-tripcountersSWITCHYARD OVERVIEW

132 kV Panels - Operations Basically there is no operation on the 132kV panels, except for the operation of thecircuit breaker remote control switchesSWITCHYARD OVERVIEW

Electric Control Room The ECR is the nerve centre of the whole power station From here the station power output is controlled and sentto the main switchyard, from where the power is distributedto the HV transmission lines as well as to the Localdistribution substations and also to the station in- plantauxiliaries As such most of the generator output controls, transformerand feeder controls, together with their protective relays andalarm indications are located in the ECR The function of the ECR also involves communicating withthe NLDC as well as liaising with the Unit Control RoomSWITCHYARD OVERVIEW

Electric Control Room The purpose of the operation, control and protection system designfor a switchyard, is to ensure that :1.The power supply is secure and remains within theaccepted voltage and frequency limits,2.The plant is protected from abnormal and sudden changesin load demand3.The plant is protected from voltage surges on the feeders orlocally due to lightning strike4.The plant is protected from over current due to earth faultsand short circuits and5.The personnel involved in the operation and maintenanceof plant are protected from danger due to mal-operation ornegligence by personnel, or due to system electrical faultsSWITCHYARD OVERVIEW

Switchyard Operation Unlike for Turbine-Generators and other machinerywhich have distinct phases of operation (such asstart-up, shutdown, etc.), the Switchyard does nothave a special start-up or shutdown The Switchyard is in operation continuously fromthe time of commissioning, except for the very rareoccasions of system breakdown which cause acomplete shutdown of the power stationSWITCHYARD OVERVIEW

Switchyard Operation We can categorize the operation of a switchyard intotwo main phases :1.Normal Operation, and2.Abnormal or System Fault OperationSWITCHYARD OVERVIEW

Switchyard Operation - Normal Operation Normally in the switchyard, the busbars are alwaysenergized, either from the machines or from the gridsystem In such rare case, the switchyard acts only asa main-intake substation, only several in the gridtransmission system Operation then merely involves the opening orclosing the feeder circuit breakers and adjustment ofInterbus Transformer tap-changers for voltagecontrol, on the instructions of NLDCSWITCHYARD OVERVIEW

Switchyard Operation - Normal Operation Normally, several machines would be running and be connected to the busbars, supplying power into the Gridsystem Therefore a major part of normal, everyday switchyard (orECR) operation is :1.The synchronising of machines onto the busbars2.The taking off of some machines from the busbars3.The synchronising of feeder CBs onto the busbars4.The taking off of feeder CBs from the busbars5.The adjustment of Interbus Transformer tap-changersto maintain the required busbar voltage and6.The adjustment of machine power and mvar output asrequired by the NLDCSWITCHYARD OVERVIEW

Switchyard Operation - Abnormal Operation or System Fault This refers to the unlikely case of a complete shutdown of the power station, and de-energisingof the busbars due to a major system faultSWITCHYARD OVERVIEW

Switchyard Operation - Abnormal OperationThe operations to follow would include ;1.Safe shutdown of machines and clearing of all circuit breakers from the busbars,2.Putting the blackstart gas-turbine onto the 132 kV barsand supplying machine auxiliaries, via the Station andUnit Boards,3.Putting the first machine back onto the busbars andproviding the load needed for its stable running, byclosing the 132 CB to supply some of the major localconsumers, and 4.Normalising the feeders by operating the appropriate CBon instructions from NLDCSWITCHYARD OVERVIEW

Disconnect SwitchAn isolator that physically isolates a circuit from all possible energy sources during maintenanceGang OperatedMechanical linkage that allows all three phases of a device to be operated togetherCapacitorAn electrical device that provides VARs when connected to the busbarsSUMMARY KEY WORDS

ReactorAn electric device that absorb VARs when connected to the busbarsBusConductors that connects few circuits together. It may be flexible conductors or hollow tubesConductorCable, transmission lines that allows power to flow from one end to the otherSUMMARY KEY WORDS

Lightning ArresterAn electrical conductor that only allows lightning (high transient voltage) to flow to groundInsulatorFix device that supports, insulate conductors, busbars and other electrical equipment in switchyardRectifierAn electrical device that converts AC power to DC powerSUMMARY KEY WORDS

SF6 :-1.Sulphur hexafluorid (SF6) is a gas that is used in GIS. It is colourless, odourless, non-flammable, not poisonous and chemically stable. 2.SF6 is a very good electrical insulator and can effectively extinguish arcs, which makes high and medium voltage apparatus filled with SF6 highly popular.SF6 is 6 times heavier than air. It may collect in cable ducts or at the bottom of tanks.SF6 is used as an insulating gas in substations, as an insulating and arc quenching medium in switchgear.Gas Insulated Substation

SF6 :-Gas insulated substation are mainly found in urban areas where you want them to take up as little room as possible. The substations reduce the magnetic field and remove the electrical field completed. This is a real advantage for installers, maintenance personnel and people who live in the vicinity of substations.SF6 has a dielectric withstand capacity that is 2.5 times better than air. At 3-5barg pressure, the dielectric strength is 10 times better than for air.Gas Insulated Substation

SF6 :-SF6 has been in use for about 40years and the service experience is very good and virtually maintenance free. SF6 impact on the environment is low.SF6 provides safe working environment for installation, operations and service personnel.SF6 does not destroy the ozone layer.The contribution of SF6 to the greenhouse effect is less than 0.1 percent of the total that mankind generates.In SF6-filled switchgear-decomposition products are created they can be handled safely and are harmless to the environment.Gas Insulated Substation

SF6 :-All SF6 gas is collected and recycled. SF6 can be cleaned and used again.SF6 can easily be destroyed.There should be no SF6 be released when equipment is erected, serviced or scrapped.Gas Insulated Substation

Operation and Maintenance GIS system :-Reduce Operating Costs. Achieved through lower SF6 loss and fewer call-outs. Manpower for unnecessary SF6 top-ups is a large but avoidable cost. Improve Reliability. Achieved through reducing risk through having fewer live top-ups.Extend equipment life. Achieved through improved gas quality and improved diagnostics capabilities.Protect the environment through reduced SF6 emissions.Improve Safety. Achieved through effective on-site SF6 analysis and improved safer SF6 Handling Practices.Gas Insulated Substation

Operation and Maintenance Handling guides :-Classifications for switching and non-switching equipment types along with indoor and outdoor applications.Risks, warning signs, and written instructions for various low-, intermediate-, and high-risk situations as well as abnormal operating conditions.Handling procedures for equipment commissioning, maintenance, and failure situations, with information on the use of gas carts for temporary SF6 storage during maintenance tasks.Gas Insulated Substation

Operation and Maintenance Handling guides :-Personal protective equipment, with emphasis on clothing and respiratory devices.Disposal and environmental protection practices for clean and contaminated SF6 gas as well as solid decomposition products under normal and abnormal conditions.Cylinder transportation, handling, and storage, focusing on DOE Regulations.Latest and emerging techniques dealing with utility related SF6 recycling and analysis issues.Gas Insulated Substation

THE ENDCopyright by Koh/Cheng