Density refers to the mass per unit volume of a particular substance under a particular condition. SF6 gas in SF6 appliances is sealed in a fixed container. At the rated pressure of 20℃, it has a certain density value, within the range of various allowable conditions for the operation of electrical appliances. Although the pressure of SF6 gas changes with the temperature change, but the density value of SF6 gas remains unchanged.
Because the insulation and arc extinguishing performance of SF6 relay largely depends on the purity and density of SF6 gas, it is particularly important to detect the purity and density of SF6 gas. The SF6 gas density meter is used for monitoring, and the gas density relay is used for control and protection.
The indicated value of the SF6 gas density meter should be in units of density. However, the indicator value of the density meter produced and used internationally at present is the unit of pressure MPa.
SF6 gas density relay is an indispensable and important accessory of SF6 circuit breaker and SF6 combined electric appliances. Its basic function is to monitor the sealing status of SF6 appliances in operation and whether there is air leakage.
SF6 relay is dominated by metal pipe, gear mechanism, pointers and double metal parts. In fact, it is on the basis of the structure principle of the metal tube pressure gauge, add a double layer metal sheet as a temperature compensation device according to the change of the ambient temperature, so that the metal tube and double layer metal sheet with the change of temperature expansion increment is equal and reverse superposition, so that the density reading does not change with the change of the ambient temperature.
SF6 relay is actually a pressure relay with temperature compensation, and its density value is represented by the corresponding pressure value of 20℃. When the temperature changes, the spring tube and double metal sheet change at the same time, so that the pointer display is unchanged.
In the case of constant volume, any pressure change caused only by temperature change can be compensated by corresponding changes of spring tube and double layer metal sheet at the same time, so it will not cause pointer deflection and ensure the correctness of indicator value of SF6 relay.
The response of the pressure element to any pressure change which is not caused by temperature change will be translated into the gas density relay pointer action and reflected on the dial, and the minimum or maximum pressure value exceeding the system can be monitored.