The Effect of Current Harmonic on Overcurrent Relay

Overcurrent relay is an important protective device for protection in power system. It can clear the large fault current quickly and easily coordinate with circuit breaker. The maximum load current that an equipment can endure during continuous operation may also have a fault and various disturbance. This condition will lead to overcurrent and malfunction equipment. The variety of loads also will influence the sinusoidal waveform, which comes out from harmonic distortion. This article investigated the effects of current harmonic on overcurrent relay. The performance of overcurrent relay is analysed with laboratory experiment. The laboratory experiment that consists of non-linear load current which have different total harmonic distortion (THD) to obtain such results. It can be concluded that a relay malfunction will occur and they will trip in a wrong sequence when affected by harmonic. The higher number of THD, the tripping current also getting higher.