| Summary: | Abstract At present, observing the temperature rise of composite insulators is an effective method for the detection of decay‐like defects. However, ambient humidity will affect the temperature rise of composite insulators, which will cause problems in screening the decay‐like composite insulators. Therefore, it is urgent to study the temperature rise principle of decay‐like insulators and find out the influence mechanism of humidity on temperature rise. In this study, a four‐electrode system is designed to measure the surface current, volume current and interface current of the decay‐like short sample and the intact short sample under different humidity. Then the equivalent circuit models of short samples and the 500 kV full‐size decay‐like composite insulator are built to analyse the contribution rates of leakage conductance loss and polarisation loss to temperature rise. The results show that the contribution rates of the polarisation loss to the temperature rise of two samples are 35.8% and 23.6% in low humidity, while they are 98.3% and 64.4% in high humidity. For the full‐size decay‐like composite insulator, the contribution rates of polarisation loss to its temperature rise in high or low humidity are more than 99%. In addition, the proportion of polarisation loss increases at first and then decreases with the increase of the length of the decay‐like section. The conclusions of this study provide a theoretical basis for further understanding the corresponding relationship between decay‐like defects and temperature rise and improve the detection rate of decay‐like insulators.
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