Ring Main Unit Gas Leakage Problem
What happens if there is gas leakage in the ring main unit?
- When the proportion of SF6 is reduced to 40%, the dielectric strength will be reduced, resulting in safety accidents, and the sealing problem must be highly valued.
- When the water content in SF6 steam is less than the saturation value at the temperature, the water is stored in SF6 steam. The experiment proves that the dielectric strength energy foundation of SF6 power switch will not be harmed at this time.If the moisture content of the steam exceeds the saturation state value, part of the water vapor will solidify in the solid insulation surface layer inside the power switch, so as to reduce its working voltage along the surface flashover, the power switch arc extinguishing characteristic is also harmful.
- SF6 gas leakage will cause environmental pollution.
Background
With the improvement of manufacturing technology, gas leakage of ring main unit is basically detected and removed in the production, processing and manufacturing, delivery experiments, handover, operation and maintenance and other important links, but it cannot be completely avoided. The main reasons for sf6 leakage include: poor production process, shell with sand holes, poor quality of sealing materials, poor quality of field assembly, sealing surface processing is not timely, vibration occurs in the operation of machinery and equipment, sealing material aging and so on.
There are 14 methods to detect gas leakage in the ring main unit
(1) Soap bubble method: Wipe the soapy liquid at the suspected point, check whether there is bubble, thus distinguish whether there is SF6 gas leakage.
Pros and cons: The monitoring method is simple and clear, which does not require expensive instruments and equipment, but the monitoring precision is poor, the monitoring is one-sided, and the monitoring period is long, which is not suitable for general measurement.
(2) Wrapping method: the plastic bags are strapped at the suspected point, and after the standard time of stalling, the concentration of SF6 gas at the strapping position is monitored by the quantitative analysis detector to determine whether there is leakage.
Pros and cons: It can complete quantitative analysis and monitoring, but it is very easy to be affected by working temperature, air pressure, shape of strapping plastic bags, testing equipment, etc.
(3) Vacuum method: For distribution equipment insulated with SF6 gas, which is not inflated, each part of the machine and equipment is vacuated to about 133Pa, and is placed statically for 4h and above. After monitoring, whether the vacuum degree is reduced or not, it is determined whether there is leakage.
Pros and cons: It is mainly used in factory monitoring, and it can not complete electrification detection, the application limitations are relatively large.
(4) Halide measurement: The application of metal platinum "halogen effect" to determine whether the detection point is leakage.
Pros and cons: It can quantitatively analyze and calculate the leakage rate, gas concentration value and other basic parameters of the leakage point, but the measurement accuracy is not high.
(5) Ultrasonic method: under the condition of the same temperature and pressure, finding the concentration of the gas to be measured can be converted into finding the average sound velocity of the mixture, by the method of phase difference for measuring sound velocity. That is, pulse counting starts at the same time of sending ultrasonic waves, and pauses counting until the amplitude value of echo signal is detected beyond a certain threshold, and then multiplies with the counting period to obtain the ultrasonic propagation duration. The fixed propagation distance divided by the duration is the speed of sound.
Pros and cons: the measurement accuracy is affected by vibration, noise and ultrasonic attenuation in the gas medium.
(6) Acoustic wave method: The characteristics of sound propagation in SF6 gas is less than that in the atmosphere for monitoring.
Advantages and disadvantages: The monitoring method is simple and clear, but the accuracy is very low, subject to the percentage of SF6 gas in the regional environment.
(7) Gas-sensitive semiconductor method: the change of resistance value after gas absorbed by gas-sensitive semiconductor is used to judge the type and concentration of gas absorbed, so as to distinguish whether leakage occurs.
Advantages and disadvantages: the application history is relatively long, the relativity of technical application is relatively perfect, and the monitoring accuracy is not bad.
(8) Electrochemical method: The electrochemical gas detector was used to measure the current value, and the concentration value of SF6 gas in the surrounding area was calculated indirectly.
Pros and cons: High measurement accuracy, but the sensor is easy to outlet saturation, and zero drift will increase with the improvement of measurement accuracy.
(9) Thermal conductivity detector method: according to different vapor bodies, the resistance value of thermistors changes differently, and the current in the monitoring circuit also changes. According to the current transformation value and the thermal conductivity coefficient of the vapor body, SF6 vapor body concentration value can be calculated.
Pros and cons: The monitoring results are greatly affected by the airflow stability, so the monitoring results are not intuitive and must be measured and analyzed, which is not applicable to the field application.
(10) Tracer method: Using the absorption characteristics of SF6 vapor, adding substances that can be absorbed by SF6 molecules to mark, and indirectly measuring the concentration of SF6 vapor.
Pros and cons: high precision monitoring, auxiliary steam must be used, only for laboratory scientific research, not practical operation in the field.
(11) Humidity sensor method: The leakage point, leakage rate and severity will be confirmed by using the characteristics of temperature and humidity transition at the leakage point and the positive correlation between the transition and leakage rate.
Pros and cons: high requirements on the accuracy of temperature and humidity sensors, and no typical application examples, only in the theoretical basic research link.
(12) UV ionization: The leakage is determined by comparing the input and output wave types of the detection instrument. The lag time of the output wave type means the amount of SF6 leakage.
Pros and cons: The leakage link can be directly reflected according to the wave pattern, and the measurement accuracy still needs to be improved.
(13) Laser imaging method: laser is sent to the detected position and the reverse direction transmitted laser is fed into the laser camera imaging system. SF6 steam will absorb the laser energy and use the imaging difference caused by the reverse direction transmitted laser to judge whether there is leakage or not.
Advantages and disadvantages: it belongs to simple visual monitoring with high precision, but the laser cost is relatively high and its size is huge, so it is not suitable for field monitoring
(14) Infrared imaging method: SF6 vapor has a stronger absorption capacity to the infrared ray of the specified band than air, and the backward astigmatism imaging technology is selected to do the imaging well.When SF6 vapor appears in the monitored range, because SF6 vapor has a strong absorption function for infrared light in the band of 10.3~10.7 m, the infrared energy reflected to the detection instrument is greatly weakened due to the absorption function, SF6 vapor appears on the screen of the analyzer whether there is air leakage phenomenon.
Rockwill Ring Main Unit：https://www.cnrockwill.com/indoor-ring-main-unit