Evaluation of chirp detector-based travelling wave localization of earth faults in MV networks

In this paper, a chirp detector of the current waveforms is evaluated for locating the earth faults in unearthed MV networks where it is used to precisely localize the travelling wave arrival times created by the fault occurrence. Chirp modulation, or linear frequency modulation employs sinusoidal waveforms whose instantaneous frequency increases or decreases linearly over time. These waveforms are commonly referred to as linear chirps or simply chirps. Earth faults in unearthed MV networks will spark a chirp signal which is starting at a high frequency then gradually decreasing to a small frequency. A simple chirp detector is used to demodulate the frequency modulated waveform resulting in a signal peak which is used to locate the fault by a time of arrival method. The evaluation is carried out considering practical modelling of current transformer (CT) where the CT is modelled covering its high frequency characteristics. Also, the network noises are added to the simulated current waveforms. The simulation is performed in the ATP/EMTP program where it is pre-processed using ATPDraw.