Study on Abnormal Heating Mechanism of Composite Insulators with Typical Defects

In recent years, abnormal heating failure of composite insulators occurs frequently in China, which brings hidden dangers to the safe operation of power grid. In order to study the abnormal heating mechanism of composite insulators, the temperature rise experiments of 500 kV composite insulators and short-string composite insulators with artificial simulation defects are carried out respectively. The effects of umbrella cover contamination, interface air gap and water intrusion on abnormal heating of composite insulators are systematically discussed. The results show that the abnormal heating of composite insulators can be divided into two main types: 1) temperature rise at high voltage end; 2) temperature rise at non-high voltage end. The former is heat source on the umbrella sleeve, which is caused by polarization loss of polar groups and invading water caused by aging of umbrella sleeve; and the latter is mainly caused by resistance loss of conductivity defects, which include polluted umbrella sleeve, sheath penetration cracking and deterioration of mandrel. Usually, the heating area and temperature rise of the latter are larger than that of the former. In addition, the combined action of moisture and heat will accelerate the deterioration and moisture absorption process of composite insulators, especially when there are air gap defects at the interface of composite insulators, moisture absorption will be more rapid and intensified, and abnormal temperature rise will be higher.