Lightning Impulse Corona Characteristic of 1000-kV UHV Transmission Lines and Its Influences on Lightning Overvoltage Analysis Results

The lightning overvoltage is one of key issues in designing the insulation of transmission line and power apparatus. Usually the influence of the impulse corona is ignored in numerical analysis of electromagnetic transients in power systems due to the lack of experimental data. But the relationship between the overvoltage and the insulation size of 1000-kV ac ultra-high voltage (UHV) power systems enters the nonlinear region, and a small decrease in overvoltage will lead to a high reduction in insulation size and bring huge economical benefits. So fully understanding the corona characteristics of the 1000-kV UHV transmission line is helpful to understand the actual wave process and realize a suitable insulation design of the 1000-kV UHV system. Experiments on the lightning impulse corona characteristic of bundle conductors for 1000-kV transmission lines are carried out in the China UHV ac test base and the impulse corona Q-V curves of different bundle conductors are obtained. The results show that the impulse corona leads the increment of the capacitance of the conductor. Analysis on the Q-V curves shows that the occurrence of the positive impulse corona has a time delay after the lightning impulse voltage exceeds the corona inception voltage and the delay time is a tenth of a microsecond. At the end of this paper, a simulation model for corona based on the empirical formulas of Q-V curves fitted from the test results is proposed, and is applied to the overvoltage analysis of 1000- kV transmission line and substation. The analysis results show the lightning impulse corona has a large influence on the lightning overvoltage of the transmission line and substation.