Gas-insulated metal-enclosed switches (GIS) and gas-insulated metal-enclosed transmission lines (GIL) are one of the most important devices in the power system. They have the dual tasks of control and protection. If they failed during operation and the problem cannot be solved timely, it will cause serious damage to the grid.

Partial discharge fault is a common fault type of GIL/GIS. It is necessary to use GIS partial discharge online monitoring and fault location system to perform real-time online monitoring of GIL/GIS partial discharge signals and analyze and process the measured data and real time give comprehensive judgment of insulation status. Then repair schedule can be arranged according to the monitoring results to avoid major grid accidents caused by equipment failure and to ensure the normal operation of the system with minimum maintenance cost.

There are many reasons for the deterioration of the dielectric medium, such as ionization corrosion caused by a strong electric field for a long time, insulation wear caused by mechanical high-frequency vibration, aging decomposition of the medium caused by thermal effects, and moisture insulation. The dielectric medium is degraded, and the performance is degraded so that the dielectric breakdown has a development process, which makes the on-line monitoring of insulation practical and effective.

The system uses specialized monitoring software using advanced high-speed DSP digital processing technology. The processing technology makes the monitoring system fast and accurate, providing an economical and reliable solution for GIS online monitoring.

Through installing UHF sensor on the key components of GIL/GIS, the system collects 500MHz-1500MHz electromagnetic wave signals excited by partial discharge in real time. It also collects feature quantities such as amplitude (Q), phase (Φ), frequency (N), and cycle sequence (t) of the pulse signal that reaches the trigger condition via detection frequency reduction circuits, high speed sampling circuits and data processing buffer circuits. Event files are generated and uploaded to the expert diagnosis system for event map establishment and insulation state analysis.