SF6 gas has become an insulating and arc extinguishing medium with its excellent electrical and physical and chemical properties, and is widely used in the field of power transmission and transformation, such as SF6 transformers, SF6 circuit breakers and GIS devices.
The so-called density refers to the mass per unit volume of a specific substance under specific conditions. The SF6 gas in the SF6 circuit breaker is sealed in a fixed container. It has a certain density value under the rated pressure at 20℃. Within the range of various allowable conditions for the operation of the circuit breaker, although the SF6 gas pressure changes with the temperature, the SF6 gas density value stays the same.
The insulation and arc extinguishing performance of SF6 circuit breakers depend on the density and purity of SF6 gas, so the detection and density monitoring of SF6 gas purity are particularly important. It will be difficult for an ordinary pressure gauge to monitor the leakage of SF6 gas or to distinguish whether it is the actual leakage or the change in ambient temperature to cause the change of SF6 gas pressure.
When the SF6 gas density meter is not installed nor used, if the ambient temperature is 20℃, the pointer points to 0 MP; but if the ambient temperature is higher than 20℃, the double-layered metal belt will stretch, and its lower end will be displaced in the direction when the SF6 gas pressure is reduced, driving the gear mechanism and the pointer to move in the direction where the density or pressure indication value decreases. When the reading of the pointer is lower than 0MP, if the ambient temperature is lower than 20℃, the gear mechanism and pointer will move in the direction of increasing density or pressure indication value, and the reading of the pointer is higher than 0 MP.
When charging the circuit breaker with SF6 gas, with the gradual increase in SF6 gas pressure, the end of the elastic metal curved pipe is displaced in the direction when the pressure increases, and the double-layer metal belt is always compensated at 20°C. With the displacement in the direction when the pressure increases, the gear mechanism and the pointer are driven to move in the direction where the density or pressure indication value increases, and the indication value becomes larger. The pointer of the SF6 gas density meter indicates the pressure of the SF6 gas at 20℃, and has nothing to do with the environmental temperature change.