Internal Failure Detection Using IR Thermography and Characterization of Composite Insulators

Failure of composite insulators due to electrical and environmental degradation can lead to catastrophic failure of the whole system. Understanding the failure mechanism and its early detection remains a challenge. This study is performed on field-aged composite insulators installed in Indian railways to understand the aging and failure mechanism and develop a detection technique to anticipate the failure. The unaged and aged insulators of the same shed profile are used. A simulation study is presented to understand the temperature field distribution due to defects at the rod-housing interface. Leakage current measurement and infrared thermography are performed to measure the surface temperature rise in simulated rainy conditions. It is observed that the leakage current of composite insulators increases with age, accompanied by a rise in temperature in the shank region when the operating voltage is applied to the insulators. Further, a unique signature of leakage current waveform is observed for aged insulators. Material characterization techniques such as SEM, EDX, hydrophobicity class, TGA and FTIR have been used to understand the aging mechanism of polymeric housing. Material study reveals the gradual aging of the HTV silicone rubber housing. Based on the simulation study, leakage current measurement and thermography and physicochemical study, it is concluded that the cause of failure is the sealant failure or the weak adhesion allowing moisture accumulation at the rod-housing interface. Due to conductive channel formation at the interface allowing increased leakage current flow and electrical discharges, the temperature rises along the insulator, indicating a degraded rod-housing interface. Based on this study, a non-invasive technique comprised of leakage current measurement and temperature rise detection using infrared thermography is recommended for early detection of interface failure.