SF6 gas density relay is mainly used to monitor the change of sf6 gas density in circuit breaker. During operation, the gas density of SF6 gas density relays will deteriorate at extreme temperatures, resulting in increased errors.
At present, SF6 density relays are mainly calibrated at room temperature, and it is impossible to accurately measure the temperature of the relays under extreme conditions. When the ambient temperature decreases, the temperature compensation performance will be affected, resulting in misoperation of the SF6 density relay.
In many areas in the north, when encountering extremely low temperatures, SF6 equipment often locks and alarms. Therefore, it is of great significance to verify the data of the SF6 density relay under extreme temperature and develop a reasonable verification device.
1. Problems in low temperature verification of SF6 density relay
At present, China's major power plants, power supply companies, large industrial factories and mines have gradually begun to pay attention to the importance of the SF6 gas density relay calibration system, and gradually began to popularize applications.
Many power supply companies and other units are equipped with sf6 gas density testing equipment. However, most SF6 gas instrument testing equipment can only verify the density of SF6 gas at normal temperature. When extreme environments are encountered, various problems arise.
Common problems mainly include the following three aspects:
First, due to the quality of the calibration instrument, the temperature compensation error occurs, and a relatively large error occurs, and this error cannot be found at normal temperature;
Second, because the design structure of the calibration instrument is not perfect, in the case of extreme low temperature, the SF6 density relay will lose its proper function, and this problem cannot be found at normal temperature;
Third, due to the lack of stability in the performance of the material, with the continuous change of time, there will be a zero offset, especially in a low temperature environment, which will further increase the error.
2. Inspection of SF6 density relay in low temperature environment
Compared with the common inspection method, the low temperature inspection of SF6 gas density relay mainly lies in the difference in temperature control. For example, in the environment below -40°C, a constant temperature control box is required to create a temperature environment and keep the temperature constant.
Then put the relay into the environment, use the calibration bench and the SF6 density relay to carry out the inspection work, and finally determine the switching difference and the action value error of the contact according to the information fed back by the relay.
The specific inspection measures are:
First, according to the difference of each group of contacts, the numerical measurement is carried out in the boosting and decompressing states, respectively, and the measurement content includes the pressure value when it is turned on and the pressure value when it is turned off;
Second, before the contacts are switched, the boosting or depressing operation should be performed, and the process should be carried out smoothly, and the pressure value of the standard device should be read at the moment when the contacts are switched;
Third, when calculating the operating value error, it is necessary to compare the rated value and pressure value of the entire SF6 density relay pressure change process with each other, including overvoltage alarm, lockout and low pressure alarm. At the same time, it is also necessary to ensure that the error and switching difference conform to the relevant technology.
3. Considerations of SF6 density relays in selection
The compensation methods of density relays can be divided into two types according to different temperatures, including standard cavity compensation type and bimetal compensation type. The standard cavity compensation uses SF6 gas for temperature compensation, while the standard cavity compensation uses ambient temperature and 20°C. The difference is compensated accordingly.
When performing standard cavity compensation, the temperature is re-adjusted to make it drop to a certain level, thereby changing the state of SF6 gas in the standard cavity and causing it to liquefy, thus reducing the measurement accuracy.
Therefore, it is generally not recommended to use standard cavity compensation SF6 density relays under low temperature environmental conditions.
Compared with the standard cavity compensated SF6 gas density relay, the bimetal compensated SF6 gas density relay does not have such problems and can be used in a low temperature environment.
However, due to the linear change in its compensation capability within a certain range, low temperature calibration must be performed before use to ensure the normal use of the equipment.
When calibrating SF6 density relays at extreme temperatures, in order to timely find out the SF6-dimensional electrical problems that cannot be found at ordinary times, and improve the reliability and stability of relays operating at extreme temperatures, a constant temperature control box can be used to verify the temperature. Take control. In addition, bimetal compensated sf6 gas density relays should be used when selecting monitoring equipment for SF6 gas at extreme temperatures.
