Research On Air-gap Discharge Characteristics And Altitude Correction Of High Altitude Converter Station

For the purpose of getting air-gap discharge characteristics and altitude correction method of high altitude converter station, in accordance with±400kV DC Connection Project of Qing-Tibet Plateau, the real structure test research of the typical air-gap of converter station and rod-plane air-gap under switching impulse, lightning impulse and DC voltage superimposed with switching impulse voltage were experimentally performed at flat area and about4000m high altitude area. Discharge characteristic curves of switching and lightning impulse at AC side of converter station and DC voltage superimposed with switching impulse at DC side were given between air-gap of2.5m～4.0m.Multistage method and up and down method were studied, by which50%discharge voltage and standard deviation were calculated. Calculation model based on elastic coefficient of standard switching impulse discharge voltage was discussed and air-gap discharge voltage of phase-to-ground, phase-to-phase were calculated by the given model.The research work of altitude influence to discharge voltage was analysised and correction errors of test data by the exsiting standards and correction factors were calculated. Altitude correction methods for phase-to-ground were recommended and correction methods with linear and exponent form formulas of phase-to-phase switching impulse voltage were also given by this paper.The test results indicated that discharge voltage of rod-plane air gap were lower than that of soft line and grading ring at the same distance and it is feasible to reduce the construction cost and optimize structure by performing real structure test research. The average discharge field intensity of pre-exist DC voltage superimposed with switching impulse voltage increases with increasing DC composition and rod-plane was more influenced than soft line. The calculation results based on elastic coefficient model were approximatively equal to experimental results. The recommened correction methods and conclusions could be used as a reference during the least air-gap design of high altitude converter station.