Modern day High Voltage switchgears use SF6 (Sulphur Hexafluoride) as an insulating medium. This is usually found in the busbar chambers. Because of its good insulating properties, switchgears can be designed to be as compact as possible thus saving space in an urban environment. At the same time, the busbar chambers have to be completely sealed thus ensuring the busbars are not subject to the elements of the atmosphere. These types of switchgears are called Gas Insulated Switchgears (GIS).

 

However, it should be noted that for the SF6 gas to effectively serve its functions, it has to be of high quality. At the filling stage, a sample of gas is drawn from each chamber of the switchgear and tested for purity (% of SF6 gas), dew point (moisture content) and SO2 (signs of partial discharge). At this stage, SO2 should be practically zero as it is a new switchgear and is not in operation yet.

 

Once the switchgears are put into operation, we will need to test the SF6 gas periodically as a predictive maintenance schedule. The test results will then be analysed and trended.

 

Partial discharge activities in the chambers cannot propagate to the exterior because the chambers are completely sealed. However, its presence breaks down the composition of the SF6 gas.

 

Should there be partial discharge activity in the chambers, the SF6 gas will breakdown and combine with H2O to form HF and other Sulphur compounds. HF (Hydrogen Fluoride) is highly corrosive and will attack the insulators/bushings in the chamber and over time will lead to these failing.

 

Our company provides this test as a high level predictive maintenance service to monitor the condition of High Voltage switchgears.