Development of GIT partial discharge UHF online monitoring system

SF₆ gas insulated transformer (GIT) is widely used in the urban power grid. The establishment of partial discharge (PD) on-line monitoring system is significant to grasp the running state of GIT accurately and guide its maintenance. According to the structure and operating characteristic of the field GIT, an outer ultra high frequency (UHF) microstrip patch antenna (MPA) sensor for detecting the partial discharge in field GIT was designed, some effective methods for expanding bandwidth are utilized in the design process, such as choosing the material, thickness, adding impedance matching and multi-tuning loop. The effective working bandwidth of the antenna is 340~440 MHz, and the relative bandwidth is 25.6%, especially the maximal gain reaches 5.38dBi. MPA sensor was installed in the GIT insulator of cable section of ingoing line, fan duct, radiating pipe of 110kV and 10kV side. Online monitoring system for GIT was established and monitoring system software based on C# was developed. Through the operation of GIT substation in Xinmin street of Chongqing City, the results show that this online monitoring system can detect UHF GIT PD signal for a long time, and it provides a lot of reliable data for condition-based maintenance.