For improving reliable operation of ring main unit（RMU） in power system

an approach for on-line monitoring the insulation characteristic and bus-bar temperature rising of the RMU is proposed. The bus-bar temperature monitoring system adopts draw-out current transformer

temperature sensor and infrared transmission to solve the problem of high voltage isolation. The leakage current and dielectric loss are monitored simultaneously to judge the insulation state

and insulation aging test is conducted to verify the rationality of the determination of the parameters values as criteria. In addition

online monitoring results verify the accuracy and reliability of the on-line monitoring system.