WHY BREAKER FAILURE PROTECTION IS REQUIRED

WHY BREAKER FAILURE PROTECTION

Breaker failure protection is needed to provide protection when the circuit breaker does not correctly interrupt the fault, the breaker failure condition is known as “stuck breaker”, this breaker failure protection can be considered as the local backup protection

BREAKER FAILURE SITUATIONS

FAILURE TO TRIP

in this situation the contacts of the breaker don’t open after energizing of the trip circuit by the protective schemes, this can happen by an open or short in the trip circuit wiring or the trip coil

FAILURE TO CLEAR

In this situation, the contacts of the breaker would be open but the arc is not extinguished, and the current will flow it could be caused by the mechanical or dielectric problems

CONTACT FLASHOVER

An open breaker could lead to massive failure, it could be caused by a restrike of an opening breaker or a surge through an already open breaker

NON-FAULT RELATED FAILURES

These kinds of failures can happen for example failure to interrupt load current or mechanical failure during switching operations

BASIC BREAKER FAILURE SCHEME

This type of protection provides a means to trip adjacent current source if the protective relay detects the fault and the associated breaker fails to interrupt the fault

To monitor proper breaker operation two conditions are used they are

  • Presence of current flow in the breaker
  • Protective relay trip signal

The breaker would have failed to operate if both of these signals present for a period more than expected breaker clearing time to determine the successful operation of the breaker a delay on the pickup timer which has a time delay setting that exceeds the breaker normal clearing time and while the breaker operates properly either one or both the inputs will de-assert and it will stop the operation of the timer

BREAKER FAILURE WITH RE-TRIP LOGIC
By the help of the re-trip design, the breaker would get a second chance to trip before a breaker failure is declared

in case of circuit breakers which has two separate trip coils, if one the trip does not function well then it can be designed to activate the re-trip, this logic can be used to energize the second trip coil and the breaker is opened before declaring a breaker failure condition.

The re-trip output contacts operating speed must be accountable for the overall time delay settings, the design logic of the re-trip is independent of the normal breaker tripping scheme. If the breaker is tripped by re-trip logic there could be some fault in the initial trip path, automatic breaker reclosing can be blocked by the re-trip output breaker tripping, to allow the maintenance inspection to find the problem.

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