# Breaker Failure Relay (Back-up Protection Relay)

- Link: https://studyelectrical.com/2015/07/breaker-failure-relay-back-up.html
- Published: 2015-07-16T09:43:00+00:00

Each year as line and system loading increase and more operating companies superimpose
higher voltage transmission systems on existing facilities, the need for high-speed
fault clearing, particularly in the face of a relay or circuit breaker failure, 
is accentuated.

![Breaker failure relay](https://studyelectrical.com/wp-content/uploads/2015/07/
failure-protection-relay-circuit-breaker.jpg)

Breaker failure relay

In such instances, the answer is invariable local [back-up protection](https://studyelectrical.com/2016/06/primary-and-back-up-protection-of-electrical-relays.html)
for circuit breaker failure and, in many cases, local back-up protection for relay
failure. In some instances, the need for positive, high-speed clearing of all faults
is so acute that two separate sets of primary relaying have been employed, with 
one set arbitrarily designated as a back-up.

The primary objective of back-up protection is to open all sources of generation
to an uncleared fault on the system. To accomplish this objective, an adequate back-
up protective system must meet the following functional requirements:

 1. It must recognize the existence of all faults which occur within its prescribed
    zone of protection.
 2. It must detect the failure of the primary protection to clear any fault as planned
 3. In clearing the fault from the system, it must
 4.  * Initiate the tripping of the minimum number of circuit breakers.
     * Operate fast enough (consistent with coordination requirements) to maintain 
       system stability, prevent excessive equipment damage, and maintain a prescribed
       degree of service continuity.

Breaker failure relays are required to give a rapid trip when the primary circuit
breaker does not break properly at e.g. a [short circuit](https://studyelectrical.com/2016/03/short-circuit-causes-and-effects-application.html)
in the network. The faulty section of the network could in this way be tripped separately.

Breaker failure relays are referred to as back-up protection devices which are applied
as stoppage protection relays for the most relays. As a case in point breaker failure
relay is employed as a backup device for the differential relay of an influence 
[power transformer](https://studyelectrical.com/2014/05/difference-between-power-transformer.html)
and additionally for distance relay of a conductor.

### Why Breaker Failure?

In the fault condition of any equipment, it is expected that the circuit breaker
of this equipment will be tripped by the main protection relays of such equipment
if there is a failure in the tripping circuit of the circuit breaker or in the circuit
breaker itself.

In this case, the circuit breaker will not be tripped and so, to isolate this fault,
the bus bar at which this equipment is connected must be completely isolated by 
tripping all the equipment connected to it by a delayed time.

Then, the only connected equipment to this bus bar is the faulted one. In this case,
the faulted equipment has no current passing through it so, it is can be disconnected
manly by isolates.

### How Breaker Failure Relay Operate?

There are three conditions must be satisfied for the operation of breaker failure
relay which are

 * Tripping signals from any main protection relay of the faulted equipment are 
   exist.
 * The circuit breaker of the faulted equipment is still connected (n.o. auxiliary
   contact from a circuit breaker is used).
 * There is current passing through this equipment even if it is valued is very 
   small.

Although one of the second and third conditions is sufficient for the healthy operation
of the breaker failure relay, it is preferable to use both for more security.

[⌊Wiring diagram of breaker failure circuit⌉⌊Wiring diagram of breaker failure circuit⌉[

Wiring diagram of breaker failure circuit

The figure shows the wiring diagram of the breaker failure circuit. Tripping circuit
of breaker failure relay is similar to the tripping circuit of the bus bar protection
relay. In general breaker failure relay may use the same tripping circuit of bus
bar protection relay.

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