substation components and bus schemes

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A REPORT ON

SUBSTATION LAYOUT AND ACCESSORIES&BUSBAR ARRANGEMENT

BY:-AMIT KUMAR SINGHNEJAMUL HOQUEHEMENDRA KUMAR RAJPUTSUB. TO:-Mr. S P JAISWAL CONTENTS

Part A : SUBSTATION LAYOUT Single line diagram Substation Switchyard Accessories Lightning Arrestor CVT Earthing switch Wave trap Isolator Current transformer Circuit Breaker Power Transformer Current transformer Reactors and capacitors Other Switchyard Equipments

PLCCSCADAPART B: BUSBAR ARRANGEMENTSingle bus systemSingle bus system with bus sectionalizerDouble bus systemDouble breaker bus systemOne and a half breaker bus systemMain and transfer bus systemDouble bus system with bypass isolatorRing main bus system PART- ASWITCHYARD LAYOUTINGCLASSIFICATION OF SUBSTATIONSBased on workingGenerating substation (step up s/s)Grid substationSwitching substationSecondary substation -- a) sub transmission voltage b) primary distribution c) distribution substationBased on structureOutdoor conventional air insulated substation (AIS)Indoor substationCompressed air insulatedG I SSINGLE LINE DIAGRAM

LIGHTNING ARRESTOR Alightning arresteris a device used on electricalpower systemsto protect theinsulationon the system from the damaging effect oflightning. Metal oxide varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known assurge arrester has a high voltage terminal and a ground terminal. Current from the surge is diverted around the protected insulation in most cases to earth.

PICTURES OF SURGE DIVERTER (LIGHTNING ARRESTOR) CVT

Capacitor Voltage Transformer(CVT), Capacitance Coupled Voltage Transformer(CCVT) To step downextra high voltage signals and provide alow voltage . For measurement or to operate aprotective relay.EARTHING SWITCH

Earth Switch is used to discharge the voltage on the circuit to the earth for safety.Earth switch is mounted on the frame of the isolators. It is located for each incomer transmission line and each side of the busbar section. LINE TRAP (WAVE TRAP)Connected in series with the power (transmission) line. It blocks the high frequency carrier waves (24KHz to 500KHz) and let power waves (50 Hz - 60 Hz) to pass through. It is basically an inductor of rating in Milli henry (approx 1 milli Henry for 220 KV 1250 Amp.). It has three main components:- 1. Main coil. 2. Tuning Device. 3. Lightning Arrestor.

ISOLATOR

Disconnector orIsolator switchis used to make sure that an electrical circuit can be completely de-energised for service or maintenance. Isolator is anoff-loaddevice. Types of Isolators are1. Central rotating, horizontal swing2. Centre-Break3. Vertical swing4. Pantograph typeCURRENT TRANSFORMER

Current transformers are used for Stepping down current for measurement, protection and control.

Current transformers are of two types1. Protective CT2. Measuring CTCIRCUIT BREAKERS ACircuit breakeris an automatically operatedelectrical switchdesigned to protect anelectrical circuit from damage caused byoverloadorshort circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker.Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit.

Small circuit breakers may be manually operated; larger units havesolenoids to trip the mechanism, and electric motors to restore energy to the springs.

Different techniques are used to extinguish the arc : Lengthening / deflection of the arc : Intensive cooling (in jet chambers) : Division into partial arcs : Zero point quenching : Connectingcapacitors in parallel with contacts in DC circuits

High-voltage breakers are broadly classified by the medium used to extinguish the arc

Bulk oilMinimum oilAir blastVacuumSF6BUSBAR

Busbars receive power from incoming circuits and deliver power to outgoing circuits.POWER TRANSFORMERS

Power Transformers are used to step up or step down a.c. voltages and to transfer electrical power from one voltage level to another.SHUNT REACTORSShunt Reactors are used for long EHV transmission lines to control voltage during low load period. Shunt reactors is also used to compensate shunt capacitance of transmission line during low load periods. Usually Shunt reactors are unswitched.

SEREIS REACTORS

Series reactors are used to limit short circuit current and to limit current surgesassociated with fluctuating loads. Series reactors are located at the strategic locations such that the fault levels are reduced.SHUNT CAPACITORSShunt capacitors are used for compensating reactive power of LPF.They are used for improving the power factor. It is also used for voltage control during heavy lagging power factor loads.They are located at the receiving stations and distribution substations. They are switched on during heavy loads and switched off during low loads.

SERIES CAPACITORSeries Capacitors are used for some long EHV a.c. lines to improve power transferability.They located at the sending end / receiving end of the lines.They are provided with by pass circuit breaker and protective spark gaps.

PART B BUS BAR ARRANGEMENTCONDUCTOR USED FOR BUSESAll Aluminum conductor (AAC) All Aluminum alloy conductor (AAAC) Aluminum conductor with aluminum alloy reinforced (ACAR) Aluminum conductor with steel reinforced (ACSR)

SINGLE BUS SYATEM

Advantages:1.Simple in Design2.Less Expenditure

Disadvantages:1.In case of bus fault or bus bar isolator fault or maintenance total Substation is out of service.2.In case of maintenance of transformer circuit breaker the associated transformer has also to be shut-down. Similarly for Line also.SINGLE BUS WITH BUS SECTIONALISER

Advantages:1. One complete section can be taken out for Maintenance without disturbing the continuity of other section. 2. If a fault occurs on one section of the Bus, that faulty section alone will be isolated.Disadvantages:It will be a little more costly with the addition of one isolator and some cases with Circuit breaker, C.Ts and C&R panel.

DOUBLE BUS SYSTEM

Advantages:: Double Bus Bar Arrangement increases the flexibility of system.Disadvantages::The arrangement does not permit breaker maintenance with out interruption.DOUBLE BREAKER BUS SYSTEM

Advantages:There is no need of bus coupler as because the operation is done by breakers instead of isolatorDisadvantages:Most expensive as it involves additional breaker, CT Isolators etc for each circuit.ONE AND A HALF BREAKER BUS SYSTEM

Advantages:During any fault on any one of the buses, that faulty bus will be cleared instantly without interrupting any feeders in the system since all feeders will continue to feed from other healthy bus.

Disadvantages:This scheme is much expensive due to investment for third breaker.

MAIN AND TRANSFER BUS SYSTEM

Switching operation:1.First close the isolators at both side of the bus coupler breaker.2. Then close the bypass isolator of the feeder which is to be transferred to transfer bus.3. Now energized the transfer bus by closing the bus coupler circuit breaker from remote.4.After bus coupler breaker is closed, now the power from main bus flows to the feeder line through its main breaker as well as bus coupler breaker viatransfer bus.5. Now if main breaker of the feeder is switched off, total power flow will instantaneously shift to the bus coupler breaker and hence this breaker will serve the purpose of protection for the feeder.6. At last the operating personnel open the isolators at both sides of the main circuit breaker to make it isolated from rest of the live system.DOUBLE BUS SYSTEM WITH BYPASS ISOLATOR

Advantages:It permits breaker maintenance without interruption of power which is not possible in double bus system but it provides all the advantages of double bus system.Disadvantages:It however requires one additional isolator (bypass isolator) for each feeder circuit and introduces slight complication in system layout.RING BUS SYSTEM

Advantages:It provides a double feed to each feeder circuit, opening one breaker under maintenance or otherwise does not affect supply to any feeder. But this system has two major disadvantages.Flexibility for breaker maintenanceEach breaker removable without disconnecting load Only one breaker needed per branch,Each branch connected to network by two breakers All change-over switching done with circuit-breakers & hence flexible.