Analysis of Influence of Electromagnetic Voltage Transformer on Overvoltage of 220 kV Cable Line

Recently, there have been many breakdown faults of 220kV one-piece pre-molded silicone rubber joint. The faults occurred in the closing process of the cable line. The faulty phases are B and C. The main difference of the three-phase cable line is that the electromagnetic voltage transformer (VT) is installed in Phase A. In order to study the influence of electromagnetic voltage transformer on 220 kV cable line, the residual voltage of cable conductor and the operating overvoltage level of cable line are simulated and analyzed by ATP-EMTP. The results show that the switching over-voltage level has little to do with whether the line is equipped with VT. When the cable line is equipped with VT, the residual charge can be released quickly through the electromagnetic voltage transformer, and the reclosing over-voltage of the line is significantly reduced. In addition, for silicone rubber insulation materials, there will be space charge accumulation under the DC field of residual voltage, which will cause the change of material electric field distribution. The abrupt change of the local electric field may lead to the breakdown of the insulation.