electrical bus system and electrical substation layout | electrical engineering

26/03/13 11:07 PMElectrical Bus System and Electrical Substation Layout | Electrical Engineering

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Electrical Bus System and ElectricalSubstation Layout

There are many different electrical bus

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system schemes available but selection of aparticular scheme depends upon the systemvoltage, position of substation in electricalpower system, flexibility needed in systemand cost to be expensed.

The main criterias to be considered duringselection of one particular Bus BarArrangement Scheme among others(i) Simplicity of system(ii) Easy maintenance of differentequipments.(iii) Minimizing the outage duringmaintenance. (iv) Future provision of extension withgrowth of demand(v) Optimizing the selection of bus bararrangement scheme so that it givesmaximum return from the system.

Some very commonly used bus bararrangement are discussed below

Single Bus SystemSingle Bus System is simplest and cheapest one. In this scheme all the feeders andtransformer bay are connected to only one single bus as shown.

Advantages of single bus systemThis is very simple in designThis is very cost effective schemeThis is very convenient to operate

Disadvantages of single bus system

One but major difficulty of these type of arrangement is that, maintenance of equipment ofany bay cannot be possible without interrupting the feeder or transformer connected tothat bay.

The indoor 11KV switchboards have quite often single bus bar arrangement.



Single Bus System with BusSectionalizerSome advantages are realized if asingle bus bar is sectionalized withcircuit breaker. If there are morethan one incoming and the incomingsources and outgoing feeders areevenly distributed on the sections asshown in the figure, interruption ofsystem can be reduced to a goodextent.

Advantages of single bus system withbus sectionalizerIf any of the sources is out of system, still all loads can be fed by switching on thesectional circuit breaker or bus coupler breaker.

If one section of the bus bar systemis under maintenance, part load ofthe substation can be fed byenergizing the other section of busbar.

Disadvantages of single bus system withbus sectionalizerAs in the case of single bus system,maintenance of equipment of any baycannot be possible withoutinterrupting the feeder ortransformer connected to that bay.

The use of isolator for bus sectionalizing does not fulfill the purpose. The isolators have tobe operated off circuit and which is not possible without total interruption of bus bar. Soinvestment for bus-coupler breaker is required.

Double Bus SystemIn double bus bar system two identical bus bars are used in such a way that any outgoing orincoming feeder can be taken from any of the bus.

Actually every feeder is connected to both of the buses in parallel through individual



isolator as shown in the figure.

By closing any of the isolators onecan put the feeder to associated bus.Both of the buses are energized andtotal feeders are divided into twogroups, one group is fed from one busand other from other bus. But anyfeeder at any time can betransferred from one bus to other.There is one bus coupler breakerwhich should be kept close during bustransfer operation. For transferoperation, one should first close thebus coupler circuit breaker thenclose the isolator associated with the bus to where the feeder would be transferred andthen open the isolator associated with the bus from where feeder is transferred. Lastlyafter this transfer operation he or she should open the bus coupler breaker.

Advantages of Double Bus SystemDouble Bus Bar Arrangement increases the flexibility of system.

Disadvantages of Double Bus SystemThe arrangement does not permit breaker maintenance with out interruption.

Double Breaker Bus System

In double breaker bus bar system two identicalbus bars are used in such a way that anyoutgoing or incoming feeder can be taken fromany of the bus similar to double bus bar system.Only difference is that here every feeder isconnected to both of the buses in parallelthrough individual breaker instead only isolatoras shown in the figure. By closing any of thebreakers and its associated isolators, one canput the feeder to respective bus. Both of thebuses are energized and total feeders are

divided into two groups, one group is fed from one bus and other from other bus similar toprevious case. But any feeder at any time can be transferred from one bus to other. There

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is no need of bus coupler as becausethe operation is done by breakersinstead of isolator. For transferoperation, one should first close theisolators and then the breakerassociated with the bus to where thefeeder would be transferred andthen he or she opens the breaker andthen isolators associated with thebus from where feeder istransferred.

One and a half Breaker Bus System

This is an improvement on the doublebreaker scheme to effect saving inthe number of circuit breakers. Forevery two circuits only one sparebreaker is provided. The protectionis however complicated since it mustassociate the central breaker withthe feeder whose own breaker istaken out for maintenance. For thereasons given under double breakerscheme and because of theprohibitory costs of equipment eventhis scheme is not much popular. Asshown in the figure that it is a simpledesign, two feeders are fed from two different buses through their associated breakersand these two feeders are coupled by a third breaker which is called tie breaker. Normallyall the three breakers are closed and power is fed to both the circuits from two buseswhich are operated in parallel. The tie breaker acts as coupler for the two feeder circuits.

During failure of any feeder breaker, the power is fed through the breaker of the secondfeeder and tie breaker, therefore each feeder breaker has to be rated to feed both thefeeders, coupled by tie breaker.

Advantages of One and a half Breaker Bus SystemDuring any fault on any one of the buses, that faulty bus will be cleared instantly withoutinterrupting any feeders in the system since all feeders will continue to feed from otherhealthy bus.

Disadvantages of One and a half Breaker Bus System



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

Main and Transfer Bus System

This is an alternative of double bussystem. The main conception of Mainand Transfer Bus System is, hereevery feeder line is directlyconnected through an isolator to asecond bus called transfer bus. Thesaid isolator in between transfer busand feeder line is generally calledbypass isolator. The main bus is asusual connected to each feederthrough a bay consists of circuitbreaker and associated isolators atboth side of the breaker. There is

one bus coupler bay which couples transfer bus and main bus through a circuit breaker andassociated isolators at both sides of the breaker. If necessary the transfer bus can beenergized by main bus power by closing the transfer bus coupler isolators and then breaker.Then the power in transfer bus can directly be fed to the feeder line by closing the bypassisolator. If the main circuit breaker associated with feeder is switched off or isolated fromsystem, the feeder can still be fed in this way by transferring it to transfer bus.

Switching operation for transferring a feeder to transfer bus from main bus withoutinterruption of power(i) First close the isolators at both side of the bus coupler breaker.

(ii) Then close the bypass isolator of the feeder which is to be transferred to transfer bus.

(iii) Now energized the transfer bus by closing the bus coupler circuit breaker from remote.

(iv) After bus coupler breaker is closed, now the power from main bus flows to the feederline through its main breaker as well as bus coupler breaker via transfer bus.

(v) Now if main breaker of the feeder is switched off, total power flow will instantaneouslyshift to the bus coupler breaker and hence this breaker will serve the purpose ofprotection for the feeder.

(vi) At last the operating personnel open the isolators at both sides of the main circuitbreaker to make it isolated from rest of the live system.

So it can be concluded that in Main & Transfer Bus System the maintenance of circuit



breaker is possible without any interruption of power. Because of this advantage thescheme is very popular for 33KV and 13KV system.

Double Bus System with Bypass Isolators

This is combination of the double bussystem and main and transfer bussystem. In Double Bus System withBypass Isolators either bus can actas main bus and second bus astransfer bus. It permits breakermaintenance without interruption ofpower which is not possible in doublebus system but it provides all theadvantages of double bus system. Ithowever requires one additionalisolator (bypass isolator) for eachfeeder circuit and introduces slightcomplication in system layout. Still this scheme is best for optimum economy of system andit is best optimum choice for 220KV system.

Ring Bus System

The schematic diagram of the systemis given in the figure. It provides adouble feed to each feeder circuit,opening one breaker undermaintenance or otherwise does notaffect supply to any feeder. But thissystem has two major disadvantages.One as it is closed circuit system it isnext to impossible to extend infuture and hence it is unsuitable fordeveloping system. Secondly, duringmaintenance or any other reason ifany one of the circuit breaker in ringloop is switch of reliability of system becomes very poor as because closed loop becomesopened. Since, at that moment for any tripping of any breaker in the open loop causesinterruption in all the feeders between tripped breaker and open end of the loop.



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electrical bus system and electrical substation layout | electrical engineering

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