Condition Monitoring of Sulfur Hexafluoride Gas-Insulated Switchgear Vessel Using Smart Ultrasonic Sensor

Abstract

Gas-insulated switchgears (GISs) are more prone to functional dielectric phenomena, which can cause behavioral changes in the electrical insulation systems. Standard maintenance and operational strategy circumscribe sulfur hexafluoride gas (SF6) operational stress emissions, a formidable greenhouse gas. In the present work, an ultrasonic sensor (HC-SR04)-based monitoring system is developed to monitor SF6 gas density inside GIS vessels. The system is designed to ensure detection capability compatible with a maximum allowable SF6 leakage rate of 0.5% of nominal gas mass per annum. With the help of a simple design, the developed system offers a linear direct measurement of gas density with a quick response time (worst case 80 s), enabling trace-level detection to avoid the possibility of GIS failure because of late detection. The functional implementation and effectiveness of the proposed method have been assessed using several influential parameters like pressure, temperature, molar mass, and humidity. The efficacy of the measurement is tested for pure SF6 gas, and for the mixture of 80% N2+20% SF6 gaseous medium at high voltage AC and DC applications (up to 50 kV AC and 70 kV DC) in the laboratory as per the industry standard IEC 61850. The developed monitoring system will be suitable to ensure the safety, reliability, and efficiency of GIS by continuously monitoring the parameters like the density of SF6 gas, breakdown voltage, and temperature.