Characteristics:
Each circuit is protected by its own circuit breaker and hence a fault on a feeder/transformer does not necessarily result in loss of supply to other feeders.
A fault on a feeder or transformer circuit breaker causes loss of the transformer and feeders circuits. They may be restored after isolating the faulty circuit breaker.
A fault on a bus section circuit breaker causes complete shutdown of the substation. All circuits may be restored after isolating the faulty circuit breaker and the substation will be ‘split’ under these conditions.
A busbar fault causes loss of one transformer and all feeders on that bus section. Maintenance of one busbar section will cause the temporary outage of all circuits. Can be used only where loads can be interrupted.
Bus cannot be extended without de-energizing of half of the substation
Difficult to do any maintenance, maintenance of a feeder or transformer circuit breaker involves loss of that circuit.
Lowest cost
The introduction of bypass isolators between the busbar and circuit isolator (Figure 2) allows circuit breaker maintenance facilities without loss of the circuit. Under these conditions full circuit protection is not available.
Bypass facilities may also be obtained by using a disconnect switch on the out-going ways between two adjacent switchgear bays (Figure 3). The circuits are paralleled onto one circuit breaker during maintenance of the other. It is possible to maintain protection (although some adjustment to settings may be necessary) during maintenance but if a fault occurs then both circuits are lost. With the high reliability and short maintenance times involved with modern circuit breakers such bypasses are not nowadays so common.