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Isolated phase bus duct systems

Isolated phase bus duct systems

Vol. 4 Issue 4


The Isolated Phase Bus Duct (IPBD) is the main conduit for power distribution in a power generation facility. With current carried between the generator and a step-up transformer solely via the IPBD system, it is the undisputable critical core of any power generation operation. The need for proactive maintenance cannot be overstated in order to mitigate the risk of repairs, downtime, or catastrophic equipment failure that often occur due to lack of inspections or continual improvements.

What is an Isolated Phase Bus?

The Isolated Phase Bus (IPB) is used to carry very large currents, typically between a generator and a step-up transformer, in power generation facilities.

Each phase conductor is enclosed in its own separate grounded metal housing, with each housing separated from each other by air. By enclosing conductors in separate housings there is considerable protection from faults between the generator and the transformer. Conductors are generally hollow aluminum tubes or aluminum bars, supported within the housing on porcelain or polymer insulators. There are generally two types of housings: continuous and non-continuous, with the latter being the older design requiring more maintenance.

IPB systems are designed to carry continuous current ratings of 3,000 amperes to 45,000 amperes, and rated for voltages from 5 kV on up to about 38kV. With larger current ratings, a forced cooled system is used to blow air through the enclosures in order to maintain ANSI set temperature limits. The cooling air is then typically re-circulated through a heat exchanger before reentering the bus.

IPB systems are usually custom designed for a particular plant and can be just as unique to maintain.

Other types of bus systems include:

  • Metal-enclosed segregated phase bus
  • Cable bus duct
  • Non-segregated Phase Bus (NSPB)
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