Analysis on the defects of two capacitor isolators in DC transmission system

In the case of single pole earth loop and double pole unbalanced operation of DC transmission, there will be DC current passing through the neutral point of transformer and entering the winding, it will cause the transformer's direct current magnetic bias, which will cause the transformer's reactive power loss and noise increase. In recent years, Ningxia electric power company of State Grid of China has installed capacitance isolation device in the transformer in the area with serious DC bias to avoid the above problems. However, two cases of current limiting resistance fusing of the device were found in the inspection process. Aiming at these problems, this paper investigates and analyzes the causes of the defects of the capacitance isolation device of the two transformers, through on-site equipment inspection and theoretical calculation And laboratory verification, combined with the structure of the device itself, find out the causes of the defects, and put forward measures to eliminate such defects. The analysis results are of great significance to the safe and reliable operation of the device.