Partial discharge detection in 11.4 kV cast resin power transformer

The sensor which consists of many conductors wound on the rectangular insulated material is employed to detect partial discharge (PD) in the 11.4 kV cast resin power transformer. To examine the effect of winding on the propagation of PD-induced field, the verification tests are performed in free space. According to the structure of transformer, we simulate partial discharge occurs inside the winding and outside the winding to examine the effect of winding to the propagation of PD-induced field. The results show that the PD-induced field can pass through the winding and detected by the coil sensor. In on-line application, to detect PD, three similar rectangular sensors are installed near the surfaces of the 11.4 kV power transformer. From the amplitude variation of PD signals, the imperfect power transformer is clearly identified. However, there is not any image appear on the surface of this power transformer. After 3 years, this power transformer is completely destroyed.