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ANSI CODE : 50BF Circuit Breaker Failure

ANSI CODE : 50BF Circuit Breaker Failure

This function is designed to detect the failure of breakers that do not open when a tripping order is sent. The “breaker failure” protection function is activated by an O1 output tripping order received from the overcurrent protection functions (50/51, 50N/51N, 46, 67N, 67). It checks for the disappearance of current during the time interval specified by the time delay T.

It may also take into account the position of the circuit breaker read on the logic inputs to determine the actual opening of the breaker. Wiring a volt-free closed circuit breaker position contact on the “breaker closed” equation editor input can ensure that the protection is effective in the following situations:

  • When 50BF is activated by protection function 50N/51N (set point Is0 < 0.2 In), detection of the 50BF current set point can possibly be not operational.
  • When trip circuit supervision (TCS) is used, the closed circuit breaker contact is short-circuited. Logic input I102 is therefore no longer operational.

Automatic activation of this protection function requires the use of the program logic circuit breaker control function. A specific input may also be used to activate the protection from the equation editor. That option is useful for adding special cases of activation (e.g. tripping by an external protection unit).
The time-delayed output of the protection unit should be assigned to a logic output via the control matrix.
The starting and stopping of the time delay T counter are conditioned by the presence of a current above the set point (I > Is).

Block diagram
Block diagram – 50BF

Block diagram – 50BF

Example of setting

The example below shows how to determine the time delay setting for the 50BF function Overcurrent protection setting: T = inst. Circuit breaker operating time: 60 ms.
Auxiliary relay operating time to open the upstream breaker or breakers: 10 ms.a

Example of setting

Example of setting using SEPAM relay

The time delay for the 50BF function is the sum of the following times: Sepam O1 output relay pick-up time = 10 ms Circuit breaker opening time = 60 ms Overshoot time for the breaker failure function = 20 ms.

To avoid unwanted tripping of the upstream breakers, choose a margin of approximately 20 ms. This gives us a time delay T = 110 ms.


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