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SF6 gas is currently widely used in high-voltage equipment due to its good insulation and arc-extinguishing properties. Therefore, monitoring SF6 gas in SF6 high-voltage electrical appliances in application has important safety and economic significance.
The integrated SF6 relay is essentially a combination of pressure gauge and SF6 relay. The front end of the spring tube is added with bimetal as temperature compensation. When the density (pressure) of SF6 gas changes, the spring tube is deformed, which drives the pointer to deflect and indicate that the on the corresponding scale value.
Because the temperature compensation of SF6 relay is designed on the principle of bimetal temperature piece, it is compensated according to the ambient temperature of 20℃. Therefore, when calibrating the SF6 density meter, first ensure that when the ambient temperature is 20°C, the relative humidity is not greater than 75%. For on-site verification, the first is that the ambient temperature cannot be accurately realized, and the second is that the bimetal temperature compensation of the density meter can only be compensated approximately. From the perspective of measurement technology, it is currently impossible to measure whether the bimetal temperature compensation is consistent with the response to temperature changes. The third SF6 gas density calibrator can only perform approximate temperature compensation for SF6 gas. It is only to verify the contact action value of the density relay. Through the comparison of the original records of calibration for four years, the indication value and contact action error of SF6 relay and density meter have not changed much, and the action error of SF6 gas monitoring is controlled within 0.03 MPa, which can meet the technical requirements of the manufacturer.
According to the verification and inspection results of the substation SF6 gas density relay and density meter for many years, the operation and maintenance of the integrated SF6 relay can be controlled by the following points to realize its own function:
First of all, it is necessary to coordinate with the engineering management department and the construction department before installation to ensure that the density tables used have been verified, and the conditions are best carried out by the operation or equipment management department; and before the SF6 high-pressure equipment is inflated, so that It is helpful for the operation or equipment management department to grasp the original condition of the SF6 relay.
For the density relay marked with abs, the absolute pressure is zero, and the calibration period can be considered as three years or synchronized with the state maintenance of the main equipment. Because there is generally no anti-vibration and lubricating silicone oil in the absolute pressure gauge, the contacts and the micro switch are completely exposed to the air. In the previous calibration, it was found that the slide plate of the micro switch was jammed, and the contact did not move even when the pressure dropped to zero. Considering the environment, sealing, lubricity and other factors, it is recommended to check the density meter for a fixed period of three years, and then gradually replace it with a fully sealed SF6 relay with shock-resistant oil.
Practice has proved that when the SF6 circuit breaker is under trouble-free maintenance, Installing the density meter after disassembly can easily cause air leakage at the joint of the density meter. It has been found during work that when there is a 0.2um foreign body at the joint, it will cause a large leakage of SF6 gas. Therefore, avoiding repeated disassembly of the density meter as much as possible has a certain effect on the sealing performance of the circuit breaker.
