TYPICAL PRIMARY PLANT BUSBAR LAYOUT DESIGNS FOR HV & EHV SUBSTATIONS

These schemes are adopted based on ease of operation & maintenance, availability & reliability of

system.

DOUBLE BUS SCHEMES

Double bus bar schemes have advantage over Single Busbar schemes as it is possible to shift the

Feeder bays from one bus to another in case of a bus fault or for taking maintenance outage of a

Busbar or for expansion/addition of Feeder bays.

Three types of Double Busbar schemes are in practice commonly which is:

Single-CB Double bus scheme (Feeder bay is connected to a particular bus by means of two

Bus Isolators). This scheme has two bus Isolators per Feeder bay which have fault making

and load switching capability. CBs are used for fault breaking duty. Total loss of Substation is

prevented by means of selective switching of Bus Isolators for individual feeder bays. During

a bus fault only those feeder bays which are connected to faulted bus are tripped leaving

other feeder bays in service. After that it is possible to switch the tripped Feeder bays to un-

faulted bus. This results in brief interruption of Feeder bays on a bus fault. Such schemes will

have Bus Coupler & or Bus section CBs to minimize the impact of bus faults on number of

feeder bays. Bus couplers also are required to prevent two buses operated in ‘Electrical’

isolation (split bus) and Substation has one ‘system’ of voltage & frequency. This scheme is

used in HV & EHV Substations.

Double-CB Double bus scheme (Feeder bay is connected to a particular bus by means of two

Bus CBs). This scheme has two CBs per Feeder bay which have fault making and breaking

capability. During a bus fault only those CBs which are connected to faulted bus are tripped

leaving other CBs in service. This results in no interruption of Feeder bays on a bus fault. Bus

coupler CBs may or may not be provided in these schemes as it is common practice to close

both CBs for each feeder bay (thereby reducing the external fault current flow through CB to

one half) which results in less CB maintenance. This scheme is used in HV & EHV Substations

with critical feeder bays.

Two main and a Transfer bus scheme (this is modification of above indicated Double busbar

schemes with an additional transfer bus). This scheme will have additional bus with

additional CB(s) & by-pass isolators. This scheme allows faster restoration of system in case

of emergency by means of minimum protection and allows maintenance of Feeder bay CBs.

This is particularly used in major Power Plant Switchyards.

In all cases, in HV & EHV systems it is required to have both buses tied together electrically.