On-site Application of Partial Discharge Detection Technology in Gas-Insulated Switchgear (C-GIS)

C-GIS is the result of combining GIS technology with switchgear technology, also known as gas-insulated switchgear. C-GIS features a cabinet-style enclosure, housing three-phase high-voltage components within a welded steel box equipped with internal partitions. The interior of the box is filled with SF6 gas at a pressure slightly higher than atmospheric pressure, serving as the insulating medium. Thanks to its robust design, C-GIS is not limited by external environmental conditions and can operate reliably even in harsh settings. Currently, major international manufacturers offer C-GIS products across voltage levels ranging from 12 to 126 kV, with a particularly diverse range available for the 12–72.5 kV class.

The high-voltage power supply company operates a total of 99 units of a certain company's 35kV C-GIS gas-insulated switchgear. This type of product is commonly used abroad in neutral-point directly grounded systems with voltage levels of 12kV, 24kV, and 36kV, while domestically it is more often deployed at user substations, typically at a voltage level of 40.5kV.

As the service life of the equipment increases, the number of failures in this model product has been steadily rising. Conducting live monitoring and detection of the insulation performance of C-GIS equipment during operation is an essential method for assessing the risks associated with condition-based maintenance of C-GIS systems. Partial discharge is one of the key parameters that reflect the insulation performance of C-GIS equipment, serving as an indicator of both the early signs and specific manifestations of insulation degradation in these devices.

Currently, ground electric wave, ultra-high frequency, and ultrasonic partial discharge measurement techniques are used to detect partial discharges in C-GIS equipment. On-site partial discharge testing aims to achieve the following results: ① Whether partial discharge is present inside the C-GIS equipment; ② The precise location of the partial discharge; ③ The type of partial discharge; ④ The severity of defects in the C-GIS system, impacting its operational performance.

The degree of safety risks and the measures that should be taken. Tianjin Electric Power Company has been conducting a comprehensive 7IEV survey on partial discharge in switchgear equipment for many years, using ultra-high-frequency and ultrasonic methods to precisely locate partial discharge phenomena in C-GIS equipment suspected of showing such issues.

Practice has shown that partial discharge detection technology effectively addresses the current shortcomings of C-GIS equipment testing methods, enabling timely identification and prevention of C-GIS equipment failures, thereby ensuring the safe operation of C-GIS devices.