Partial Discharge Investigation of 22kV Distribution Transformer

This paper presents an off-line partial discharge (PD) experiment conducted on a 22 kV/400 V distribution transformer, which was decommissioned after 20 years of service. The study investigates the impact of reduced oil levels within the transformer on PD characteristics that are expected to facilitate PD activity within the transformer. The experiments were performed with reduced oil levels below the top clamp and using both single-phase and three-phase voltage excitations, with PD measurements recorded for each case. The PD signals were measured using High-Frequency Current Transformers (HFCTs) and capturing current pulses of PD in the frequency range of 100 kHz to 20 MHz. Additionally, transformer oil tests were performed, including moisture content, oil breakdown voltage, and oil conductivity. The results of the PD measurements and oil tests are introduced and discussed in this paper.