Experimental Study On Electrization's Outer Insulation In Qinghai-Tibet Railway

It has been proved that the discharge voltage of air-gap and insulator decrease due to the lower air density at high altitude both at domestic and abroad. Flashover will take place if the external insulation is not properly designed. Recommendations have been put forward for the correction of external insulation discharge voltage at 2000 m regions or below. In spite that there is no general voltage correction method at the region between 2000 m and 4000 m, investigators gave some voltage correction methods for external insulation, which should be applied depending on special situations. However, there is no report about same studies at the region 4000 m or above, and there is no method available.Among the 1136 km Qinghai-Tibet railway being under construction, 960 km of it is above 4000 m. So, it is a prominent and urgent problem to make certain selection of the tunnel headroom's insulation air-gap. We simulated air condition of over 4000 m in the cylindrical artificial climate chamber, and studied the AC, lightening impulse and switching impulse discharge performance of short rod-plane air gaps below 500 mm and short insulator strings with 25 kV supply system in Qinghai-Tibet railway as criteria. Based on the experiment results, we analyzed the discharge performance of short rod-plane air gaps and short insulator strings in the air condition of altitude 4000 m or over, and give the correction formula of short rod-plane air gaps and short insulator strings in the air condition of altitude over 4000 m. The main research works and results of this paper are as following:The discharge voltage of short rod-plane air gaps and short insulator strings will decrease with the decrease of atmospheric pressure, but the decreasing tendency is related to the range of altitude. The atmospheric pressure can be used as the characteristic parameter in token of the effect of the altitude on external insulation voltage. Our studies indicate that the discharge voltage of short air gaps and short insulator strings is the power function of atmospheric pressure ratio, as equation U=U₀(P/P₀)ⁿ(or U= U₄₀₀₀(P/P₄₀₀₀^m ,if it is based on the altitude 4000 m. The...