A novel technique for on-line PD localisation based on pulse rise-time and transfer function

A major challenge in accurately locating the source of PD activities in power cables is that PD pulses suffer from significant attenuation as they travel from their site of origin to the cable terminal where a PD monitoring system is connected. This attenuation results in detected PD signals possessing different waveforms from the original PD pulse. Identifying PD pulses, establishing the correlation between the pulse at the site of origin and that at the detection point(s), and correctly identifying the time-of-arrival for calculating location of the signal source becomes crucial. This study presents an effective PD localisation method for use in on-line cable PD monitoring system, which is based on PD pulse Rise-Time and Transfer Function (RTTF). In comparison with four other well-known location techniques, i.e. Time-Domain Reflectometry (TDR), Phase difference, Arrival Time Analysis (ATA) and Amplitude-Frequency (AF) mapping, PD localisation by the proposed RTTF method, the proposed approach can be used to localise a PD source which is further away from the PD detection point than other methods and can be used in on-line PD monitoring systems. As on-line PD monitoring sensors commonly comprise of a high frequency current transformer (HFCT) and a high-pass filter, the rise time of detected PD pulses depends on the attenuation of the cable, the HFCT used and the filter applied. Simulations of pulse propagation in a cable and PD monitoring system are performed, based on analyses in the frequency domain using the concept of transfer functions. Results of RTTF from the simulations have been verified by laboratory experiments and on-site PD measurements, which provide evidence that the RTTF method is a very valuable and useful PD localisation technique.