Due to the electrostatic adsorption of the DC line, the pollution level of the DC line is higher than that of the AC line under the same conditions. The number of insulators required is also greater than that of the AC line. Its insulation level is mainly determined by the pollution discharge characteristics of the insulator string. Therefore, at present, there are two main methods for selecting the number of insulators:
1. Use the insulator pollution tolerance method according to the artificial pollution test of the insulator, measure the pollution flashover voltage of the insulator under different salt density, and thus determine the number of insulators.
2. According to the operating experience, the creepage specific distance method is adopted. The creepage specific distance of DC lines in general areas is twice that of AC lines. Of the two methods, the former is intuitive, but it requires a large number of tests and test data, and the results of tests are widely dispersed. The latter is simple and easy, but the accuracy is poor. In practice, this two methods are usually combined to perform.
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