Effect of atmospheric pressure on discharge performance of short air-gaps at altitude of 4000 m and above

In order to supply a referred test data for the external insulation design of the Qinghai-Tibet electrization railway´s 27.5 kV power supply system, simulated the atmospheric conditions of the altitude of 4000 m and above in the artificial climate chamber, the AC and the positive lightning impulse discharge performance of rod-plane short air-gaps of less than 500 mm was carried out. According to the test results, this paper analyzes the factors influenced the discharge voltage of a short air-gap at the pressure of the altitude of 4000 m and above. And it puts forward that both the AC and the 50% positive lightning discharge voltage of a rod-plane short air-gap is a power function of the pressure, and that the characteristic index of the effect of pressure on the discharge voltage is related to the type of the voltage and the distance of the air-gap. Then it puts forward that both the AC and the positive lightning impulse discharge voltage of the short air-gap decrease 5∼6% with a rise of 1-kilometer at the altitude of 4000 m and above.