Isolated-phase bus

In electrical engineering, isolated-phase bus (IPB), also known as phase-isolated bus (PIB) in some countries, is a method of construction for circuits carrying very large currents, typically between a generator and its step-up transformer in a steam or large hydroelectric power plant.

By enclosing the conductors in separate housings a high degree of protection from two-phase and three-phase faults is obtained.

The consequences of a two- or three-phase fault between the generator and the first circuit breaker are therefore much more serious and often result in severe damage to the busbars and nearby equipment.

Some items of switchgear, such as circuit breakers and isolating switches, are made in housings compatible with the isolated-phase bus.

Some types of apparatus such as disconnecting switches, circuit breakers, and instrument transformers are made in enclosures that can be welded to become an integral part of the isolated-phase bus system.

Isolated phase bus during installation at the Bui Dam Ghana. Segments of the bus are temporarily supported by scaffolding. The interior aluminum conductors are temporarily braced for installation. The inner conductors and outer enclosure will be welded to form a unit. Inside the enclosure, the inner conductor is supported by polymer insulators; a small hatch for access to the insulator is visible. Each phase is separated.