POFBG-Based Humidity Detection Method for Insulating Gas in Electrical Equipment

The accumulation of moisture content undoubtedly threatens the safe operation of gas-insulated electrical equipment. Online humidity monitoring of SF6 is an important way to check the insulation status of live equipment. This article presents a direct optical measurement method based on a polymethyl methacrylate fiber Bragg grating (POFBG) sensor for the humidity detection requirement of SF6 gas with a very small water content. The experimental results show that this method is feasible with the sensitivity and resolution of the POFBG sensor studied being 14.3 pm/% relative humidity (RH) and 0.1% RH in the range of 8.4%-30.4% RH. Additionally, the temperature variation can affect the RH change of gas-insulated substation (GIS) and other sealed containers. Therefore, a reduction method of RH centered on the initial baseline conditions under the condition of constant water content is also proposed. It can eliminate the error in RH measurement caused by temperature variation.