Condition Monitoring of Cap and Pin Insulator String by Electric Field Mapping Using Electro-Optical Probes With FEA Model Validation

Cap and pin insulators are widely used in electricity transmission towers in power systems and are one of their key functional elements. This paper reports on a successful application of using electric field as an index to detect and locate shorted insulator units in a cap and pin string. Electro-optical (EO) probes were used to measure the electrical field, and a six axis robotic arm, holding the probes, enabled electrical field mapping at different spatial locations. The electric field distribution was first plotted according to the measurements performed by EO probes travelling along straight lines parallel to the string, and then a closer examination between insulator sheds was conducted to evaluate the possibility of higher accuracy locating of shorted insulator units. The measured changes in electric field distribution were compared with predictions from corresponding electrostatic finite element analysis (FEA) models, confirming the ability of locating shorted units in the string based on observation of the field spatial distribution change. The electric field monitoring system was also further developed to achieve operator-free and automated data acquisition and recording. The reported methodology exhibits promising potential in live condition monitoring of insulator strings in high voltage (HV) towers.