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What are the reasons why SF6 gas humidity in SF6 electrical equipment exceeds the standard?
发布时间：2016-10-27
来源：ydlcb 浏览次数：61次
In actual operation, the excessive humidity of SF6 gas often occurs. Combined with field examples, the main reasons are summarized as follows:
(1) The equipment is poorly dried, and excessive moisture is absorbed in the assembly process of the factory, such as epoxy resin support parts, tie rods, etc., adsorb moisture during the processing process, and the drying is not thorough, which will slowly be released into the SF6 gas, and the circuit breaker may bring the moisture in the air to the inside of the equipment during the production and assembly process. Although the equipment is required to be filled with high-purity nitrogen and vacuum-dried after assembly, the water attached to the inner wall of the circuit breaker chamber cannot be completely removed. In addition, the solid insulation material in the SF6 circuit breaker is mainly epoxy resin injection. The water content of these epoxy resins is generally 0.1-0.5%. These moisture in solid insulation materials can be gradually released over time.
(2) The water contained in the SF6 new gas, whether it is the SF6 new gas or the gas in the operation of the SF6 circuit breaker, will inevitably contain trace amounts of water. The water in SF6 new gas is mainly mixed in the production process. Because SF6 has to go through pyrolysis, water washing, alkali washing, dry adsorption and other processes after synthesis, there are many production links, and a small amount of water is inevitably left behind. When charging and aerating the circuit breaker, this moisture will enter the circuit breaker directly. In addition, the SF6 gas cylinder in the storage process, if the storage time is too long, the cylinder is not tightly sealed, the atmospheric water will penetrate into the bottle, and the water content of SF6 gas will increase. Therefore, according to the regulations, the humidity of the gas in the cylinder stored for more than half a year should be remeasured when filling the SF6 new gas.
(3) The flange face of the switch is not tightly sealed. If there is a certain gap between metal parts and porcelain parts, uneven, combined with grinding, the sealing surface often produces intermittent and small radial wear, which may lead to the immersion of water molecules.
(4) Water molecules in the atmosphere may penetrate the inside of the SF6 circuit breaker through the sealing weak link. General SF6 circuit breaker due to artificially controlled circuit breaker internal water content is low. The partial pressure of water vapor inside is very low, while the partial pressure of water vapor in the atmosphere is very high. Under the conditions of high temperature and high pressure, the water molecules will automatically permeate from the high pressure region to the low pressure region. The higher the temperature outside, the greater the relative humidity, the greater the internal and external water vapor pressure difference, the greater the possibility of water molecules in the atmosphere through the circuit breaker sealing weak link, into the circuit breaker. Because the diameter of SF6 molecule is 4.56×10-10m, and the diameter of water molecule is 3.20×10-10m, SF6 molecule is spherical, and the water molecule is slender and rod-like, when the water pressure difference between inside and outside is too large, the water molecule is easy to enter the circuit breaker inside.
(5) Influence of test conditions. If not in accordance with the SF6 electrical equipment in the gas management and testing guidelines GB/T 8905-1996 testing standards. The test result of humidity was not converted to the measured value at 20℃ and 0.1MPa. Another example is the instrument problem, the instrument has not been verified by the metrology institute or has expired, and the sampling system has problems such as poor sealing, poor drying, high temperature and high humidity.