A cold fog test method of composite insulators

In this paper, based on a unique environmental test chamber with refrigerating system, fog generator and AC high voltage supplier, a cold fog test method was developed to evaluate the contamination flashover performance of silicone rubber composite insulators under the winter fog condition. The main characteristics of this method are that the temperature of the chamber is controlled to cycle in the range of -1 degC to 1 degC with the period of about 50 minutes. An AC test voltage is applied to the sample and raised to flashover at the rate of 3 kV/s when temperature reaches 2 degC in a cycle. The test is continued until the flashover voltage at a cycle is higher than the previous one. A type of short-string composite insulators was investigated using this cold fog method and the conventional steam fog method, respectively. NaCI and kieselguhr were chosen as pollutants and the pollution degree was 0.2/2.0 mg/cm². For the samples with different initial hydrophobicity, the test results show that the flashover voltages in the cold fog test are 13%-26% lower than that in the steam fog test. It confirms that the winter fog performance of composite insulators should be investigated using the cold fog method at ambient temperatures near 0 degC