Partial Discharge Location for Cast-Resin Transformer by UHF Partial Discharge Sensor and Pulse Waveform Identification
As the technique of on-line partial discharge measurement gets more precise, the goal of early warning is reached and the insulation breakdown is prevented. Besides the prevention of insulation breakdown, how to avoid the same defected equipement occurs again also attracts one's attention. As the defect is detected at low partial discharge level, the deterioration is at the early stage and the insulation material is possible not to be damaged yet. In such situation, it is hard to find the defect by dissecting defected equipment without partial discharge location.
For gas-insulated switchgear and oil-immersed transformer, there are several effective methods for partial discharge location. However, there is no effective method of partial discharge location for cast-resin transformer. However, the cast-resin transformer is broadly used in industries due to its small size and free maintenance, and it is importance to develop an effective method to locate partial discharge source.
The methods of partial discharge location for gas-insulated switchgear and oil-immersed transformer could be applied on cast-resin transformer, but, however, it would induce relatively large error because of the compact design of cast-resin transformer whose size is relatively smaller than GIS and power transformer. Although these methods are more suitable for cast-resin transformer than traditional method does, the suspected defect area is large due to the limitation of measuring instrument.
Authors modified the differential method, which compares the strength of measured signals to indicate the partial discharge location, and improved its performance by means of the adoption of UHF partial discharge sensor and the identification of the pulse polarity. The signal to noise ration is hence to be increased by UHF partial discharge sensor, and the location accuracy is also enhanced by the adoption of the identification of the pulse polarity of partial discharge signals.
One defected cast-resin transformer is taken as example to explain how this method works, and the defect is indistinguishable due to the early stage of deterioration. The mentioned method located the partial discharge source in a small area and the investigators can focus on the small suspected area to find out the partial discharge source easily. The analyses of sanning electron microscope and energy dispersive spectrometer confirm the defect discovered by this method.
Since the defect is discovered, the improvement of equipment could be made and the preventing recurrence of defected equipment could be also achieved. The field experience shows the mentioned method of partial discharge location is practicable and has good performance.