The impact of current transformer saturation on the performance of differential protection of generators and motors at frequencies below 50 Hz

Abstract

At present, low-frequency modes are widely used in the operation of electric generators and engines. Relay protection should ensure the implementation of its functions even at a frequency below the rated by tens of percent. Signals from current transformers go to inputs of current relay protection devices, and their performance deteriorates significantly at frequencies below industrial. The article experimentally investigates the impact of the core saturation of a current transformer that occurs at low frequency on the value of the differential current in the differential relay protection circuit of a generator or motor. The authors analyze how the burden of current transformers, the value of the current and its frequency affect the value of the differential current. They show the possibility of both a false response and a failure in the operation of the differential protection at low frequency. Moreover, the authors give practical recommendations on ensuring emergency protection of equipment at a frequency below 50 Hz.