Single Bus Arrangement: 1st Option

The main and transfer bus configuration connects all circuits between the main bus and a transfer
bus
(sometimes referred to as an inspection bus). Some arrangements include a bus tie breaker and others
simply utilize switches for the tie between the two buses.
This configuration is similar to the single bus arrangement; in that during normal operations, all
circuits are connected to the main bus.
So the operating reliability is low; a main bus fault will de-energize all circuits.
However, the transfer bus is used to improve the maintenance process by moving the line of the circuit
breaker to be maintained to the transfer bus. Some systems are operated with the transfer bus normally
de-energized. When a circuit breaker needs to be maintained, the transfer bus is energized through the
tie breaker.
Then the switch, nearest the transfer bus, on the circuit to be maintained is closed and its breaker and
associated isolation switches are opened. Thus transferring the line of the circuit breaker to be
maintained to the bus tie breaker and avoiding interruption to the circuit load.
Without a bus tie breaker and only bus tie switches, there are two options:
1st option
The first option is by transferring the circuit to be maintained to one of the remaining circuits by
closing that circuit’s switch (nearest to the transfer bus) and carrying both circuit loads on the
one breaker.
This arrangement most likely will require special relay settings for the circuit breaker to carry
the transferred load.
2nd option
The second option is by transferring the circuit to be maintained directly to the main bus with
no relay protection from the substation. Obviously in the latter arrangement, relay protection
(recloser or fuse) immediately outside the substation should be considered to minimizefaults on
the maintained line circuit from causing extensive station outages.
The cost of the main and transfer bus arrangement is more than the single bus arrangement
because of the added transfer bus and switching devices. In addition, if a low-profile
configuration is used, land requirements are substantially more.
Connections of lines to the station should not be very complicated. If a bus tie breaker is not
installed, consideration as to normal line loading is important for transfers during maintenance. If
lines are normally operated at or close to their capability, loads will need to be transferred or
temporary generators provided similar to the single bus arrangement maintenance scenario.
The main and transfer bus arrangement is an initial stage configuration, since a single main bus
failure can cause an outage of the entire station.
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As load levels at the station rise, consideration of a main bus tie breaker should be made to
minimize the amount of load dropped for a single contingency.
Another operational capability of this configuration is that the main bus can be taken out-of-
service without an outage to the circuits by supplying from the transfer bus, but obviously, relay
protection (recloser or fuse) immediately outside the substation should be considered to
minimize faults on any of the line circuit from causing station outages.
Application of this type of configuration should be limited to low reliability requirement

situations.
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 dosing 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.
References:
 Air-Insulated Substations — Bus Switching Configurations / Michael J. Bio

 Substation layout and accessories and busbar arrangement – Amit Kumar, Nejamul
Hoque and Hemendra Kumar Rajput

Single Bus Arrangement: 1st Option

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The main and transfer bus configuration connects all circuits between the main bus and a transfer

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Application of this type of configuration should be limited to low reliability requirement

 Air-Insulated Substations — Bus Switching Configurations / Michael J. Bio

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