Busbar Protection & Frame Leakage Protection Working Principle

Bus bar Protection:

The busbars are an important power distribution part in the power system. They are built inside of the panel with safe condition. The busbar faults are very rare but if occurs there could be seviour damage in other electrical installation. Hence the fault in the busbar section must be isolated immediately. The busbar protection must be fast, stable and reliable. The busbar protection is responsible for protecting the panel associates electrical apparatus such as circuit breakers incoming and outgoing pole contacts, isolating switches including earth switches, potential transformer, current transformer etc.

Fault in the Busbar:

  1. Bus bar insulation material deterioration.
  2. Circuit breaker failure.
  3. Earth fault due to failure of support insulator.
  4. Flashover due to sustained excessive over voltages.
  5. Errors in the operation and maintenance of switchgear.
  6. Earthquake and mechanical damage.
  7. Accidents due to foreign bodies falling across the busbars.
  8. Flashover due to heavily polluted insulator

Two types of Busbar protection are implemented…which are

Frame Leakage Protection of Busbar:

Frame Leakage Protection of Busbar is used to protect the busbar, circuit breaker, isolator switches instrument transformer from busbar earth faults. All Busbar used in a power system is neatly bound with PVC insulation or other high voltage insulation material. PVC protects the busbar from earth faults. The switchgear framework is also insulated from lead cable sheaths.

In this, the bus bar supporting frame will be earthen through a current transformer. When the fault in busbar, the fault current flow through supporting frame’s earthing arrangement. The Current transformer in the earthen frame reads the fault current and if this fault current higher than the pickup current, then the relay operates.

Frame Leakage Protection of Busbar
Frame Leakage Protection of Busbar


At that same time, the transformer neutral is connected to ground through the current transformer. However, the fault current in the busbar frame reach his source through the neutral of the transformer as shown in the figure, hence the same current will be read by the neutral CT. This neutral CT operate the tripping contact. Here The contacts of check relay (neutral leakage relay) and frame leakage relay are in series. Thus before tripping circuit gets energized both the relays must operate. Once both the relays operate due to earth fault, all the breakers will trip connecting the equipment to the busbar. Due to check relay, accidental operation of single relay to trip the circuit gets avoided.

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