High impedance fault detection based on current harmonic analysis using Chirp Z transform

High Impedance Fault (HIF) is a problematic fault of feeders which its fault current is lower as compared to normal current in power system. Likewise, due to magnitude of impedance engaged in fault area and behavior of fault current is specific and not the same as the usual fault current profile which cannot be identified by standard relays. The HIF is created whenever a live conductor contacts with objects owning large impedance. The HIFs Signal has high index of similarity with some normal cases in feeders like Nonlinear loads (NL) waveform, or instant of switching of linear loads (LL), capacitor banks (CB) and full load transformers (FLT), which provided methods must distinguish them. So, the paper utilized a novel method with ability of recognizing HIF from all possible events in feeders with high accuracy. The Chirp Z Transform (CZT) has been applied to extract the features of HIF and/or other usual network events signal. It is possible to appropriately detect fault by low order harmonics of current signal extracted by means of CZT. Maximum discrepancy of detection is nearly 7 ms which is accurate enough. Also, absence of threshold values in algorithm makes it simple and can be used in each type of distribution and even transmission systems. Working in low-frequency harmonics is another advantage of this method because needs lower sampling frequency. The evaluated signals of HIF, NLs, LLs, capacitors and FLT are acquired by a simulated 13.8 kV distribution system in MATLAB/Simulink.