Double Bus, Double Breaker.
The double bus, double breaker scheme
requires two circuit breakers for each feeder circuit. Normally, each
circuit is connected to both buses. In some cases, half the circuits
operate on each bus.
This scheme provides a very high level
of reliability by having two separate breakers available to each
circuit. In addition, with two separate buses, failure of a single
bus will not impact either line.
For these cases, a bus or breaker
failure would cause loss of only half the circuits, which could be
rapidly corrected through switching. The physical location of the two
main buses must be selected in relation to each other to minimize the
possibility of faults spreading to both buses.
The use of two breakers per circuit
makes this scheme expensive; however, it does represent a high degree
of reliability.
Maintenance of a bus or a circuit
breaker in this arrangement can be accomplished without interrupting
either of the circuits.
This arrangement allows various
operating options as additional lines are added to the arrangement;
loading on the system can be shifted by connecting lines to only one
bus.
A double bus, double breaker scheme is
a high-cost arrangement, since each line has two breakers and
requires a larger area for the substation to accommodate the
additional equipment. This is especially true in a low profile
configuration.
The protection scheme is also more
involved than a single bus scheme.
Below is the diagram of a double bus
double breaker substation scheme:
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