Comparative Study on Residual Current Signal Processing Method of AC/DC Sensitive Residual Current Transformer

AC/DC sensitive residual current transformer (AC/DC RCT) is used to detect residual sinusoidal alternating currents, residual pulsating direct currents or residual smooth direct currents and the characteristics of AC/DC RCT is of great significance for residual current protection under complicated waveform conditions. An AC/DC sensitive residual current transformer based on magnetic modulation principle as well as its Mathematical simulation model is proposed. Based on this, different signal processing methods which are about the simulation of residual current waveform signal are studied and compared. Firstly, based on the analysis of operation principle of AC/DC RCT, a computer based simulation model is established. Secondly, based on the Fourier transform, Spectrum analysis about five typical residual current signals, which include full-wave signal, half-wave signal, quarter-wave signal ,135° wave signal and smooth direct currents signal and comparison about the spectrum are obtained. Thirdly, Approaches of signal processing on the complex waveforms, which is represented the actual residual current on the protected circuit, have been studied. And the FIR low-pass digital filter with suitable parameters is concluded to be the most suitable method for the signal processing of AC/DC sensitive residual current transformer. Finally, conclusion that FIR low-pass digital filter is the most suitable device to process the residual current signal of AC/DC sensitive residual current transformer has been reached.