Improved design of grounding transformer to facilitate partial discharge online test

Summary

Analyze the cause of the accident of 10kv dry-type grounding transformer in 110kv transformer substation .Through fault analysis and disassembly analysis and other means to determine the cause of the fault is the grounding transformer body winding in the process of B-phase Y-winding coil between the inter-turn and inter-layer short circuit, the inter-layer short circuit coil temperature increased significantly, resulting in the surrounding of the epoxy insulation material decomposition, resulting in combustible gases.Cause the grounding transformer has a certain percentage of PD,and combined with the recent occurrence of many ground fault in Beijing ’ s grounding transformer accident,pointed out that the importance of live detection in grounding transformer .Grounding transformer’s existing structure can not be detected on-line,then a method of improving the grounding transformer is proposed, which is favorable for the detection of partial discharge.UHF,HF, ultrasonic, infrared four detection methods were simultaneously detected, while the use of the traditional laboratory PD monitoring instrument monitoring the discharge capacity.Under the same conditions, no effective signal was detected by UHF, ultrasonic and infrared detection methods, and the detection effect of high frequency method was obvious.In the high-frequency partial discharge detection, select four locations for PD detection in the grounding transformer test circuit. The ground line of the cable between the neutral point of the grounding transformer and the small resistance boxes got good detection results,so do 10kV cable terminal bifurcation in grounding Transformer side.Taking into account the latter's security,we select the previous position for detection.In this area can effectively detect 200pC discharge capacity of the grounding transformer,and extend the ground wire does not affect the result.Taking full account of personnel and equipment safety during the PD test and the convenience of the transformation process, it is suggested to connect the neutral point of the grounding transformer and the grounding resistance to a single core flexible cable.One end of the cable ’ s metal shield is grounded,the other end does not.The method is favorable for on-line monitoring of grounding transformer.And the new method reduced the accident rate.

Additional informations

Authors

Y. HAN, M. SUN

Keywords

Grounding Transformer, Online Test