Lightning Impulse Flashover Performance of Non-Uniform Pollution Insulators

Flashover of pollution insulators is a serious threat to the safe operation of transmission lines, and most existing researches are limited to the AC and DC flashover performance of non-uniform pollution insulators and the lightning impulse flashover performance of uniform pollution insulators. The lightning resistance of pollution insulators is lower than that of clean insulators, and under natural conditions, insulators show nonuniform pollution state, which exacerbates the electric field distortion and has a greater impact on the flashover voltage. To address the shortcomings of existing researches, this paper carries out lightning impulse flashover tests on 7 pieces of XP-70 and LXY-70 suspension insulators with non-uniform pollution top and bottom surfaces after preloading AC voltage in Xuefeng Mountain Energy Equipment Safety National Observation and Research Station of Chongqing University.Firstly, the inert and conductive components of pollution are simulated using diatomaceous earth and sodium chloride, and the ratio of non-soluble deposit density (NSDD) to equivalent salt deposit density (ESDD) on the surface of insulators is maintained at 6. The top and bottom surfaces of insulators are coated separately using a quantitative painting method, and different non-uniform pollution accumulation ratios (TIB) are simulated by keeping the total amount of sodium chloride on the surface of insulators constant and only changing the salt density ratio on the top and bottom surfaces of insulators. After the test arrangements are complete, the lightning impulse circuit switch is disconnected, and the AC circuit switch is closed and preloading AC 70 kV voltage to insulators. After 3 minutes of preloading AC voltage, the AC circuit switch is disconnected and the lightning impulse circuit switch is immediately closed. The up and down method is used as the test voltage addition method, and the voltage step is set at about 3% of the expected lightning impulse flashover voltage t/50% and 20 valid tests are conducted on the same sample.The results show a very obvious polarity effect and a polarity reversal phenomenon. When the TIB is 1:1, the negative polarity lightning impulse flashover voltage of insulators is higher than the positive polarity lightning impulse flashover voltage; when the T/B is 1:8 and 1:15, the positive polarity lightning impulse flashover voltage of insulators is higher than the negative polarity lightning impulse flashover voltage. At the same value of ESDD, as T/B decreases, the leakage current under preloading AC voltage is also reduced, while the lightning impulse flashover voltage of insulators shows an increasing trend, and the positive polarity lightning impulse flashover voltage of insulators increases more than the negative polarity lightning impulse flashover voltage. In addition, an ultra-high speed camera with an exposure time of 10 μs, a frame rate of 90 000 and an exposure of 5 is used to film the flashover process of the XP-70 insulators at an ESDD of 0.08 mg/cm2 and a T/B of 1:8. The filmed flashover process shows that many discontinuous local arcs exist on the surface of insulators before flashover and the discontinuous local arcs are all formed on the bottom surface of insulators. As time progresses, the stable local arcs develop rapidly along the surface of insulators and eventually lead to a flashover. Finally, according to the form of lightning impulse flashover of non-uniform pollution insulators, the equations of lightning impulse flashover voltage gradient for ordinary porcelain and glass suspension insulators are established and verified, with the verification results showing that the relative errors between the calculated values and the test values of XP-100, XP-120, LXY-100 and LXY-120 insulators are within ±6.56%. © 2023 Chinese Machine Press. All rights reserved.