Application Example of SF6 Gas Density Online Monitoring System

GIS (Gas Insulated metal-enclosed Switchgear) is a high, precise, and advanced power transmission and distribution equipment that has developed in recent decades. It requires less maintenance and has high operational reliability, making it widely applied in power plants and substations.

In GIS equipment, SF6 gas is commonly used as insulation and arc extinguishing medium. Existing GIS equipment generally lacks online monitoring systems, which means it cannot detect SF6 gas leaks and their development trends in a timely manner. This can result in accidents that endanger the safety of the main equipment, causing damage and affecting the stable operation of the system.

In recent years, with the rapid progress of sensing technology, microelectronics, and computer technology, various SF6 monitoring systems for GIS equipment have emerged. Especially in large-scale power projects both domestically and internationally, remote SF6 gas density relay online monitoring systems have been gradually applied. This article will introduce the application of SF6 density monitoring systems in GIS equipment using the example of the Sonla hydroelectric project in Vietnam.

Function of SF6 Monitoring System

In the Sonla hydroelectric project in Vietnam, remote SF6 gas density relays are used in the online monitoring system to collect SF6 gas state parameters in each compartment of the GIS. This allows for real-time and remote monitoring of SF6 gas density during the operation of the GIS, as well as historical data analysis, strengthening monitoring measures, and better ensuring the safety and stable operation of the equipment.

Components of SF6 Monitoring System

The complete GIS gas density online monitoring system mainly consists of remote SF6 gas density relays, relays, and conversion modules, and on-site service computers.

This system first collects the pressure and temperature in high-voltage electrical equipment through pressure and temperature sensors in the remote SF6 gas density relays. It then converts them into standard 4-20mA DC signals and outputs them to the lower computer. The lower computer (relay and conversion module) uses its internal C51 microcontroller to calculate and process the collected standard 4-20mA DC signals into density values. Finally, the density values are uploaded to the upper computer (on-site service computer) in the substation control room through the RS485 bus.

The upper computer uses industrial control configuration software to control the central system, receiving and displaying the temperature, pressure, and density values transmitted by the lower computer. The upper computer control center system processes and displays the data, sets alarm values and lock values, issues alarms when gas leakage occurs, and realizes storage and query of historical data and trend curves.

After the installation of the Sonla hydroelectric project's GIS gas density online monitoring system, the entire system continuously monitors the gas density of 177 compartments in the 500kV GIS system and 31 compartments in the 220kV GIS system. Since its operation, the system has been stable and has repeatedly monitored and alarmed the drop in SF6 pressure in the 200kV GIS equipment in a timely manner.

Through engineering practice, it has been proven that SF6 pressure monitoring is an indispensable monitoring method for GIS equipment. With the extensive application of GIS equipment in the power system, SF6 gas density online monitoring systems in GIS will be increasingly promoted and used. Replacing mechanical pointer density sensors with GIS SF6 gas density online monitoring systems will become an inevitable development trend, and GIS SF6 gas density online monitoring systems will become one of the standard configurations for GIS equipment.

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