Review on the Characteristics,Heating Sources and Evolutionary Processes of the Operating Composite Insulators with Abnormal Temperature Rise

This paper reviews the research progress on abnormal temperature rise(ATR)of composite insulators.The ATR of composite insulators can be divided into two types,point-form temperature rise(PFTR)and bar-form temperature rise(BFTR).The composite insulators with PFTR only show significant temperature rise at high relative humidity(RH)(>70%),and the temperature rise is located in the area that is 20 cm above the metal end-fitting.In a low humidity environment(<30%),there is little temperature rise(<1.0 K).The polarization loss on the surface of the silicone rubber housing under an AC electric field after moisture absorption is the main heating source.Corona discharge in high RH causes surface degradation of the silicone rubber.The composite insulators with BFTR shows significant temperature rise at both high(>70%)and low(<30%)RH.The temperature rise could reach more than 10◦C and the temperature rise area is wider,extending from the high-voltage end to several shed units at the lowvoltage side.And the glass fiber reinforced plastic(GRP)core in the composite insulator is found to be corroded.The heating energy is supplied by both conductance loss and polarization loss of the corroded GRP core.The decay-like degradation of the GRP core is caused by the combination of damp conditions,high electric field,discharge,mechanical load,et al.and may evolve into a decay-like fracture of the composite insulator.The preventive methods concerning quality control,structure optimization,material modification and operational strategy are presented.It is suggested that when PFTR is detected on the composite insulator,the inspection period of the insulator should be properly shortened.The composite insulator should be replaced as soon as the BFTR was detected.