Tests on the first 500 kV compact transmission line in China

The paper deals with the tests on the first 500 kV compact transmission line in China. The transmission line is located in north China power network. It is from Fangshan substation to Changping substation near Beijing. The transmission distance of the line is 83 km. In order to investigate the characteristics of the transmission line, many tests were performed on the line before and after its operation. The electrical parameters including the positive sequence and zero sequence impedance were measured before operation. The results are the same as the designed ones. The electrical field near the transmission line when it is energized is not higher than the conventional transmission line. As compared with the conventional transmission line, the insulation distance of the compact transmission line is considerably short; the switching surges of phase to earth and phase to phase were investigated carefully during switching operation. Different operation modes of the breaker are considered. The phase to earth overvoltage is less than 1.79 p.u. The phase to phase overvoltage is not greater than 3.45 p.u. The voltage and current unbalance between the phases of the transmission line is very small when it is energized. The audible noise and radio interference is not higher than the designed one.