Obviously in the latter arrangement, relay protection (reclose or fuse) immediately outside the substation should be considered to minimize faults 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 3.5 Double Bus—Single Breaker Arrangement The double bus—sing]e breaker arrangement connects each circuit to two buses, and there is a tie breaker between the buses. With the tie breaker operated normally closed, it allows each circuit to be supplied from either bus via its switches. Thus providing increased operating flexibility and improved reliability. For example, a fault on one bus will not impact the other bus. Operating the bus tie breaker normally open eliminates the advantages of the system and changes the configuration to a two single bus arrangement (Figure 3.4). Relay protection for this arrangement will be complex with the flexibility of transferring each circuit to either bus. Operating procedures would need to be detailed to allow for various operating arrangements, with checks to ensure the in-service arrangements are correct. A bus tie breaker failure will cause an outage of the entire station. The double bus—single breaker arrangement with two buses and a tie breaker provides for some ease in maintenance, especially For bus maintenance, but maintenance of the line circuit breakers would still require switching and outages as described above for the single bus arrangement circuits.