(1) Necessity of transformation of three-way connection module of SF6 gas density relay
The SF6 relay, like other pressure gauges, will have a certain drift in its alarm and locking values after a period of use. In addition, the temperature compensation material will have a large error in its alarm and locking values due to aging and deformation after a period of use. In addition, the contact action of density relay may be insensitive or ineffective because of infrequent action. This hidden danger will directly lead to the failure to timely alarm or lock when the pressure in the SF6 switch drops to the alarm or lock value due to gas leakage, resulting in a major accident. Therefore, the SF6 relay should be calibrated regularly.
(2) Calibration cycle requirements of SF6 gas density relay
The calibration time required by the regulation is: 1 to 3 years. After overhaul or if necessary, the specific calibration time is set by the pilot laboratory of each province, and the calibration time is generally once every 2 years.
(3) Relevant provisions of the relevant departments of the State on the addition of TEE joints
The connection mode between SF6 relay and switchgear body shall meet the requirement of not disassembling the density relay for calibration.
(1) Remove SF6 relay on site for calibration, mainly to calibrate the accuracy and correctness of the action of alarm and locking pressure contact of density relay.
(2) Cut off the power supply of the control loop of the density relay.
(3) Remove the density relay and put it in static position for 2 hours (why static position is required: make the elastic deformation of the sensitive element in the pressure gauge return to normal).
(4) Connect the contact socket of density relay calibrator to the corresponding contact of the measured density relay.
(5) Use the density relay calibrator to raise the SF6 gas pressure to the rated pressure of the density relay, and then slowly reduce the SF6 gas pressure until there is the closing contact action of the SF6 relay. At this time, record the pressure indication value of the SF6 gas density standard table on the density relay calibrator and record the value (the pressure value at 20℃). Repeat this for 3 times, and take the average value of the 3 times as the result of the final locking pressure value of density relay. According to the precision grade of density relay, whether the average value is within the accuracy range of the factory locking pressure value is judged. From steps 3 to 5, the entire test took about 20 minutes.
In conventional calibration methods of density relay, frequent disassembly of density relays increases the possibility of equipment damage and air leakage. Meanwhile, disassembly and installation of density relays takes a long time, and it takes about 10 minutes for skilled personnel to disassemble and install density relays.
Therefore, it is particularly important to install an online calibration valve without disassembling between the switch body and the density relay. With the online calibration valve, the density relay can be calibrated without disassembling the density relay, which not only saves the calibration time, but also avoids the risk of the sealing surface leakage caused by the installation and disassembling of the density relay.