Heating phenomenon in unclean composite insulators

• Phenomenon of abnormal temperature rise on composite insulator
• Moisture and surface filth mutually influence the degree of heating.
• Heating on polluted composite insulators is led by polarization loss and LC.
• Silicone rubber aging degree also affects the degree of heating.

Abnormal heating phenomenon may be the precursor of fracture on composite insulator in the transmission line. In this paper, in order to study abnormal heating phenomenon of composite insulators during regular inspection, two operating composite insulators which had been in service for six years in 500 kV transmission line, and a new composite insulator of the same type, were inspected by infrared imaging tests. To understand the characteristic of temperature gradients varying with pollution level and relative humidity (RH), infrared imaging and leakage current of the samples with different amount of pollution placed in the climatic chamber were monitored. The results show that uneven heating along the housing occurs on the high voltage end. With the increase of the pollution level, the phenomenon of temperature rise becomes severer. What's more, RH was found to play an important role with the heating phenomenon. By analyzing the results of temperature rise under different RH with various levels of pollution, the abnormal heating on the polluted composite insulators was found to be caused by polarization loss of the water absorbed by the interface of the housing and resistive leakage current induced by pollution on the high voltage end.