| ±800kV UHVDC transmission lines have high voltage level, and its transmission environment is complex, so the pollution characteristics of its external insulation have been widely concerned about. Up to now, the operating experience of the UHVDC transmission system is scarce at home and abroad. The research about the external insulation of transmission line and converter station with such high voltage level of ± 800 kV is in great need. Also, the work in regard to the pollution classification of the DC system is also in the exploratory stage.Based on the ± 800 kV Haminan- Zhengzhou UHVDC transmission line in Henan province, the comparative natural pollution test concerned of energized and de-energized insulators was carried out. According to the experimental results, we obtained the value and variation rule of the contamination on insulators of the UHVDC negative conductor in this region, as well as the influence of the electric field. Then, According to the contamination components of the negatively energized insulators, and combined with the enrichment factor method, the effect of the pollution sources around the tower to the contamination of the insulator is analyzed.At the same time, we carried out pollution measurements of post insulators under the condition of +800k V, +400kV,-800 kV,-400 kV DC and 500 kV AC fields in Zhongzhou converter station. In the measurement, we targeted post insulators with different insulation materials like porcelain, composite and coating RTV, in order to study their contamination characteristics contrastively. It turns out that the pollution is more severe at Polar II(negative) side than at Polar I(positive) side, and the severity is in connection with the insulation material. For composite and RTV coated post insulators, on average, ESDD at Polar II is 2.4 times at Polar I and NSDD at Polar II is 2.7 time at Polar I.Based on the existing contamination test results of Hazheng line in Henan province and the pollution severity of AC lines in the surrounding area, and combined with the AC saturation coefficient and ratios of contamination degree under DC stress to under AC stress proposed by the present researches, we classified the pollution level and drew the map of polluted areas of Hazheng transmission line in Henan province. For the pollution-tested region, the DC pollution level should be determined by AC saturation coefficient and the ratio of contamination degree under DC stress to under AC stress. The coefficient and the ratio can be taken as 1.6 and 1.5 respectively. For transmission tower without operation experience and pollution data of adjacent DC lines and DC transmission system in similar surroundings, much less site pollution severity data of DC energized insulators of its own, the pollution level can be determined according to the ratio of contamination degree under DC stress to under AC stress, plus the pollution data of AC transmission lines nearby or in similar surroundings.Besides, In order to compare the contamination deposit difficulty of suspension insulator of different materials and profiles in inland area and then provide reference data to the insulation design and selection, a one-year natural pollution experiment under de-energized condition was carried out on Miping overhead line, Henan. The Dixon test is first suggested to detect the outliers in natural contamination datasets, which helps to determine the effective range of pollution level of insulators. Via Shapiro-Wilk test(S-W test) and normal quantile(Q-Q) plot, the normality of the tested insulators' relative contamination values(ratios of measured contamination values of tested insulators to that of the XP-70 insulator) is testified. This establishes the theoretical basis to the method of using relative contamination values to characterize the pollution character of insulators. Then the calculating method of proper values(relative contamination values) of insulator character is given. |
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