SOLUTION

Bus coupler is a device that is used to couple one bus to the other without any interruption in the power supply and without creating hazardous arcs. A bus coupler is a breaker used to couple two busbars in order to perform maintenance on other circuit breakers associated with that busbar. It is achieved with the help of a circuit breaker and isolators.

Main and Transfer Bus Arrangement

The main and transfer bus arrangement has two buses: one is the main bus, and the other is the transfer bus. With the help of isolator switches, it is connected to the transfer bus, which is called bypass isolators and with the help of circuit breakers and isolator switches, it is connected to the main bus. A bus coupler is also required in this arrangement, as shown in Figure.

In normal conditions, the feeders are fed through the main bus, but during fault conditions, the load is transferred to the transfer bus. To transfer load from the main bus to the transfer bus, we need to close the bus coupler first and then close bypass isolators of the feeder to be connected to the transfer bus. Then we must open the isolator switch off the feeder coupled to the main bus and then open the bus coupler breaker.

When the maintenance on any breaker is required then there is a changeover frown main bus to transfer bus and controlled through bus coupler breaker. The system uses an additional isolator on each circuit which increases the cost of the system As the changeover from the main bus to the transfer bus in this system is through isolators, careful interlocking is necessary with the bus coupler breaker.

Advantages:

• It ensures supply in case of a bus fault. In case of any fault in a bus, the circuit can be transferred to the transformer bus.
• It is easy to connect the circuit from any bus.
• The maintenance cost of the substation decreases.
• The bus potential can be used for relays.

Disadvantages:

• Requires one extra breaker for the bus tie
• Switching is somewhat complicated while maintaining a breaker.
• Failure of the bus or any circuit breaker results in the shutdown of the entire substation.