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50 - Instantaneous or Definite Time Overcurrent Relay (1-ph)


The instantaneous or definite time overcurrent relay (50) operates when the current it monitors goes beyond the specified overcurrent pick-up value for a specified time delay. The operating quantity of the relay can be the RMS value of a phase current, or the positive, negative or zero sequence of a three-phase current signals. If the input is over the pickup value for the specified Time Delay, the function asserts the output Trip of 1 (otherwise 0).

Icons and diagrams

Model overview

The 50P element is defined as an instantaneous phase overcurrent element if the time delay is set to zero.  When setting a non-zero time delay, the element is set as a definite-time overcurrent element. If and only if the measured current becomes larger than the pickup value for a longer duration than the preset time delay, an overcurrent situation is asserted and the relay sends a trip signal through 50P. Otherwise, the element's internal timer is reset and the relay does not trip. 


The below figure shows the control panel of the 50P relay.

The following parameters are tunable: 

Parameter tab of 50P Relay

NameUnitDescriptionSample Value
Pick up currentpu or AThe overcurrent limit value. The units should be the same as that for the input signal5 pu
Time delaysecTime delay after which the output (Trip) becomes HIGH if input remains greater than the pickup current sec0.3 

Input and output signals
The module has 1 input and 1 output:

50P Relay I/O

I/O NameType (Unit)Description
Ipu or AA single dimensional signal, it should be the RMS value of phase current, or the positive, negative or zero sequence of a three-phase current signals.
TripBinaryThe output of 50 overcurrent relay. By default it is 0, if an overcurrent scenario is detected, it becomes 1

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