Analysis and Suppression Method of No-load Ultra High Voltage Transformer Resonance Overvoltage and Inrush Current

In order to study transient characteristics of closing no-load ultra high voltage(UHV) transformer on the 1 000 kV side and to get the magnitude of overvoltage and inrush current,so as to provide technical basis for operation of closing no-load transformer,we compared actual measurement results with calculated results of UHV AC pilot project,and obtained reasonable transformer excitation curve and remnant magnetism value,which could improve accuracy of simulation model.Moreover,we simulated and computed the closing no-load transformer.Results indicated that voltage of excitation curve should not be low,and the remnant magnetism value should be chosen between 40%~50%.The chosen transformer excitation curve and remnant magnetism value were applied to the extension project of UHV AC pilot project,and the overvoltage and inrush current while closing no-load UHV transformer on the 1 000 kV side were calculated.Results showed that the probability of resonance overvoltage of closing UHV transformer was higher than that of 500 kV transformer,and there was no resonance overvoltage while closing UHV transformer in Changzhi or Jingmen Substation,however,the resonance overvoltage of per unit value was higher than 1.3(reference value(2×1 100/3) kV) while closing the second transformer at Nanyang substation.In addition,the closing resistor could effectively restrain resonance overvoltage,and the inrush current was small.