Before the test, the high and low temperature control box can be used to control the temperature between -40°C and +60°C, and then perform accurate inspection work. In order to connect the data, it is necessary to combine the control box and the platform to effectively adjust the pressure and temperature of the air source between them. The calibration software will automatically read and store the test value according to the temperature, including contact action value and contact return value. Since there is a certain curve relationship between the pressure value and the temperature, the change of the relationship between the two can be used to judge whether the relay action value is qualified. The technical characteristics of the calibration equipment include the following three aspects: First, the equipment has an SF6 gas charging system, which can help SF6 relay test samples to replenish gas conveniently and quickly; second, the equipment has two sensors at the same time, which are relative pressures sensors and absolute pressure sensors. Since there are many types of SF6 density relays, the function of these two sensors is to measure the value of different types of relays. The following issues should be paid attention to during the debugging process:
1. Ensure the accuracy of the pressure value reading
In the process of testing, it is found that the value on the SF6 relay does not match the pressure value collected by the system, and there is a considerable error. The reasons for this problem are:
Firstly, because the thickness of the pipeline is prone to large changes, so the pressure transmission is relatively unstable, which makes the instantaneous pressure unbalanced;
Secondly, if in a low temperature environment, the pressure indication values of the density relays at the near and far ends of the air supply port do not match, and the near end is greater than the far end, it means that the distance between the installation position of the 4 density relays and the air supply port is not equal;
Thirdly, because the position of the density relay is far away from the position of the pressure sensor, the phenomenon of not reading the value in time will occur.
For these three problems, specific improvements can be made to the pipeline, such as: replacing the mounting frame of the density relay, adjusting the position so that the distance between the relay position and the air supply port position is equal; adjusting the pressure sensor installation position, and changing it to the relay near the proximal end of the sensor to improve the timeliness and accuracy of pressure reading.
2. Ensure the accuracy of the temperature value reading
Adjust the temperature in the high and low thermostat control box to -40℃, and then put the density relay in it for two hours before testing. During the inspection, it was found that the temperature value read by the system after adjustment was -33°C instead of -40°C. The reason for this phenomenon is that SF6 gas will liquefy as the pressure rises, and then release a certain amount. The heat makes the test temperature near the gas path higher than the adjusted temperature. In order to make the actual ambient temperature reach -40°C, the position of the temperature sensor should be adjusted to keep it away from the gas path.
3. SF6 relay calibrator, calibration station
Density relay calibrator is also called SF6 relay calibrator, sulfur hexafluoride density relay calibrator, which is mainly used for the calibration of pressure and action indicators of density relays. It has the advantages of less gas consumption, fast test speed, and high test accuracy. It is widely used in substations, power plants, and major power maintenance departments.