| During the start-up and commissioning of UHV transmission and transformation project in China,the flashover fault of bus basin insulators occurres many times during the charging switching test of GIS no-load bus.The analysis shows that the residual voltage of GIS bus makes the surface area of bus basin insulator accumulate charge,and the combined action of residual voltage and closing impulse voltage will produce complex charging transient overvoltage.The superposition of DC and impulse overvoltage will reduce the insulation level of GIS bus.Therefore,it is necessary to study the influence of DC superimposed impulse voltage on UHV GIS bus insulation.This study has important practical significance for improving the insulation level of GIS bus and ensuring the safe operation of substation.The main research contents are as follows.(1)The DC superimposed impulse voltage test circuit is designed,and the GIS bus test platform is developed.The test circuit is mainly composed of impulse voltage generator,DC voltage generator,protection resistor,DC isolating capacitor,resistance capacitance divider and GIS bus test platform.The simulation calculation of the protection resistor and DC isolating capacitor in the test circuit shows that the protection resistor is 500kΩ,the length of external insulation is 10 m,the resistance wire adopts double winding method,and the grading ring is added to optimize the external insulation structure.The DC isolating capacitor is 30 n F and the external insulation length is 10 m.A 1100 k V series550 k V GIS bus test platform is developed.The observation window and voltage measuring device are designed for the test platform,which can observe the discharge phenomenon and measure the discharge voltage in real time.(2)When the interior of GIS cavity is clean,separate lightning/switching impulse voltage test and DC superimposed lightning/switching impulse voltage test with different polarity and different amplitude are carried out.Each polarity combination is tested for10 times,and the results are compared and analyzed.The results show that: When separate± 2400 k V lightning impulse voltage test and separate ±1800k V switching impulse voltage test is tested separately,the 550 k V GIS bus did not flashover.In the 30 tests of-2400 k V lightning impulse voltage superimposed over-225 k V DC voltage,11 flashover occurred on 550 k V GIS bus.The lowest lightning impulse voltage is-1716.52 kv,and the amplitude is 28.5% lower than-2400 k V.In 30 tests of-1800 k V switching impulse voltage superimposed over-225 k V DC voltage,550 k V GIS bus flashover occurred twice.The lowest switching impulse voltage is-1684.74 k V,and the amplitude is 6.4% lower than-1800 k V.From the test results,it can be seen that the flashover voltage of GIS bus decreases in the superposition test of negative DC and negative lightning/switching impulse voltage,and with the increase of negative DC voltage amplitude,the superposition impulse voltage amplitude and the superposition value of both decrease.(3)When the GIS cavity is not clean,DC superimposed switching impulse voltage test is carried out,and the results are compared and analyzed.The results show that when there are non-metallic foreign bodies in the GIS cavity,the-450 k V DC voltage is applied in advance and then superposed separately ±1800k V switching impulse voltage,no bus flashover occurred;When there are metal foreign bodies in GIS cavity,the amplitude of superimposed switching impulse flashover voltage is-1050 k V after the-450 k V DC voltage is applied in advance,the amplitude is 41.7% lower than-1800 k V.The test results show that the non-metallic foreign matter has no obvious effect on the flashover voltage of GIS bus,while the metallic foreign matter can significantly reduce the insulation level of GIS bus. |
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