Characteristics of multi mode sensor for partial discharge signal monitoring in oil insulation

Abstract

Partial Discharge (PD) is a term used to describe electrical discharge activity which is normally accompanied by sparks. PD can occur when electric field difference across the void exceeds the minimum breakdown field strength. Therefore, PD measurement and diagnosis is an important nondestructive technique for assessing the quality and integrity of high voltage transformer. In practice, PD measurements suffer from noise interference due to low sensitivity of available sensors. Noisy signal at the output of the sensors cause inaccuracy in the detection of PD. In this work a multimode optical fiber sensor would be used to detect PD in transformer because it has the advantages such as: small size and weight, enormous potential bandwidth, immunity to interference and crosstalk, and compare it with electrical(capacitive) sensor. PD was detected at atmospheric pressure in voltage range (0-20 kV), the output from these two detection processes and the source wave form fed into separate channels of the multichannel digital oscilloscope. The gained data has been analyzed in time and frequency domain by using (OrginPro8) software. These results show that the appearance of PD caused a ripple in the shape of source wave form and it is being more clear in high voltage rang where in time domain these results show that signal generated by PD contains a sinusoidal pulses. The shapes and peaks of the signal output of both sensors follow the same oscillatory pattern at the same time with the ripple in the source wave form. Although these shapes and peaks of the signal output of both sensors are not much clear in voltage range below (20 KVp-p) but in voltage range above (20 KVp-p) the optical sensor shows good sensitivity where it shows up clear peaks and more than the capacitive sensor and this conclusion approved by the Frequency Domain Analysis the Fast Fourier Transform (FFT) where optical shows good resolution in range of voltage above (20 KVp-p).