Partial Discharge Location in Cast Resin Transformer by Multiple Small Loop Sensors

In epoxy cast resin power apparatus, there exist unexpected insulation defects of voids and delamination. Existence of such defects can generate partial discharge (PD) with degradation of the epoxy, which eventually leads to electrical breakdown with crucial damage to the insulation systems. Thus, early PD detection and specifying the location for such defects is important. This study presents PD location in epoxy cast resin transformer of rated voltage of 6.6 kV by detecting electromagnetic (EM) wave emitted by PD using several small loop sensors. As a result, it was found that the signal intensity and arrival time difference of EM wave detected with two loop sensors can confine the defect area. Furthermore, the arrival order of EM waveforms by sensor position was measured using arrayed four loop sensors, which can locate PD in more detail. Other experimental results on PD location using X-ray irradiation to the cast resin transformer including voids was found to correspond to that provided by the present four loop sensors' PD location method. In addition, the advantage of defect location of LS was confirmed by comparison with other sensors.