A New Method to Discriminate the Inrush Current Based on Prony Analysis

The main problem for transformer protection is still how to identify inrush current. The inrush current is likely to occur when the transformer is closed with no-load or when the voltage recovers after fault. False operation may take place for the inrush current is big enough. This paper takes prony analysis as tool to fit the current waveform, and finds that there are two attenuation factors in asymmetrical inrush current's aperiodic component, one attenuation factor in fault current's aperiodic component, zero attenuation factor in symmetrical inrush current's aperiodic component. It is necessary to point out that the two attenuation factors in asymmetrical inrush current are very different in value. Thus, it is possible to identify the inrush current through the number of aperiodic component's attenuation factor. A large number of MATLAB simulation results prove the method.