Substation/Switchyard Bus and Breaker Arrangement/Configuration Reliability, Flexibility and Cost Comparison
This arrangement involves one main bus with all circuits connected directly to the bus. The reliability of this type of arrangement is very low. The maintenance of the bus and breakers would require the outage of the total system and the line.
Double Bus, Double Breaker
This configuration provides a very high reliability by having two separate available to each circuit but a high capital cost.
Main and Transfer Bus
Since all circuits are connected to a single, main bus, reliability of the system is not very high. However, with the transfer bus available during maintenance, de-energizing of the circuit can be avoided. This arrangement is slightly expensive than the single bus arrangement, but does provide flexibility during maintenance.
Double Bus, Single Breaker
In this arrangement, a failure on one of the bus will not affect the other bus. However, a bus tie breaker failure will cause the outage of the entire system. Cost is comparable to the Main and Transfer Bus configuration
For a failure on a circuit, the two adjacent breakers will trip without affecting the rest of the system. However, a breaker failure or breakers that fail to trip will require adjacent breakers to be tripped to isolate the fault. Maintenance on a circuit breaker in this scheme can be accomplished without interrupting any circuit. The cost is also comparable to Double Bus, Single Breaker scheme and Main and Transfer Bus scheme.
Breaker and a Half
This configuration has the highest reliability and flexibility during maintenance, but, ultimately, has the highest cost.