Temperature distribution characteristics and heat defect judgment method based on temperature gradient of suspended composite insulator in operation

In order to solve the problem of determining the heating suspended composite insulators in transmission lines, infrared tests for composite insulators newly put into operation and with heat defect were conducted. The insulator surface temperature distribution characteristics were obtained. Furthermore, the characteristic parameters based on temperature gradient were revealed and the judgment method of heating defect was established. The results indicate that considerable proportion of the composite insulators in operation have a temperature difference more than 5 K, thus false judgment could occurred when judging heating defect only by temperature difference. Normal composite insulator temperature curve was composed of high-frequency and low-frequency components. The influence of the low-frequency component on the temperature difference is greater than that of the high-frequency component. Obvious temperature gradient exists at the heating region boundary. The standard deviation of temperature gradient and the maximum absolute value of temperature low-frequency component gradient are effective characteristic parameters to distinguish whether heating defects exist. The heating defect judgment method was established based on the characteristic parameters, and was verified by field data with an accuracy rate of 94.31%. The method satisfied the heating defect judgement under UAV infrared lens with spatial resolution value not larger than 0.895 mrad.