Liu Shuxin

Development of on-line monitoring system of switchgear

For improving reliable operation of switchgear in power system, an approach for on-line monitoring the insulation characteristic and bus-bar temperature rising of the switchgear is proposed in this paper. Through comparing several existing temperature measurement methods for monitoring temperature rising elevation at bus-bas, a new design of temperature monitoring method is proposed. It adopts quick-magnetic saturated current transformer, temperature sensor and infrared transmission to solve the problem of high voltage isolation. For switchgear insulation characteristic monitoring, using the micro-controller unit (MCU) and hardware design, an on-line dielectric loss angle and leakage current measuring method with low cost and high accuracy is implemented. Sensor and signal conditioning circuit design are adopted to ensure the accuracy of leakage current measurement. The frequency voltage signal is extracted by connecting voltage-dividing capacitor on capacitive device terminal and absolute method of measurement and zero-crossing comparison measurement is adapted to measure dielectric loss angle whose principle and calculation approach are presented in this paper. The leakage current and dielectric loss angle can be regarded as criterion to assess switchgear insulation characteristic. Because the monitoring system works in several electromagnetic interference environments, some hardware and software electromagnetic immunity measures are discussed. At last, the system runs in real system and the result shows the on-line monitoring system is stable and reliable which can be provide reference for on-line monitoring system design of switchgear.