Study On The Principle And Method For On-line Monitoring Of Moisture Content In SF₆ Circuit Breaker Gas

When moisture content in SFg Gas-insulator switchgear reaches to a certain extent,It could be compounded with product of SF6's decompose under arc action and then produces poison which results in chemic corrupt. At the same time,it also arouses the drop of insulated performance and bring on flashover of insulated surface. The electrical and mechanical characteristic is influenced by moisture content,as well as the badness would happen.This paper studies the source,change rule and quantitatively harm of moisture content in SF6 gas. Based the humidity theory,the paper adopts the relative humidity as the character value and puts forward using 30%RH and below 0C dew-point as the on-line monitoring critical value. It gives the method of volume ratio convert at the different temperature. With the standard value,we can conclude the result of moisture content.The paper studies the present situation and characteristic of sensors and brings forward using macromolecule polyimide-based capacitive humidity sensor in on-line monitoring system which has physical adsorption and can continuously measure between 0 to 100C. By adopting the method of saturated aqueous salt solutions,the paper designs the equipment to produce the humidity source and scale PI sensors. Based on the design and long period measurement of demarcated equipment,we get the lots of curve and data that shows the linear relation between capacity and moisture and good linearity and resolving power.According to disposal and analysis of sample data,it brings forward the principle and method of digital measurement-frequency measurement and designs the hardware system. The circuit suit for long-distance transmission and monitoring and has high precision and anti-jamming characteristic. It measures the frequency by PCI card which is base on the method of multi-period synchronization.The paper studies the mechanism of the monitoring system and gives it's structure. Considering the practice,the software is compiled which is based on win98 DLL and used to control the sample and disposing data. As the same time,temperature compensation,curve fitting,fuzzy theory and data amalgamation are applied to ensure the precision of measurement and advances the veracity.The simulated experiment results show that the on-line monitoring system can present the variation of the moisture content in the SF6 gas and provide a good technique for on-line monitoring system.