On-line partial discharge detection in transformer

This paper describes an on-line partial discharge (PD) detection technique applicable to distribution transformers. This technique uses a spectrum analyzer with a high-frequency preamplifier and high-frequency current probes. The PD measurements normally are made on each of the primary and secondary windings with a high-frequency current transformer clamped around the cables below the bushing of each winding. This technique is capable of detecting PD activity in the range of 100 kHz to 200 MHz. The on-line PD detection technique was used alongside the Dissolved Gas Analysis (DGA) technique to check the insulation integrity of several transformers. This paper describes the results of these test methods applied on seven 300 kVA transformers. These transformers show different levels of deterioration with the DGA concentrations in the range of 44 to 5,042 ppm and PD activity ranging from 15 to 1,800 pC