On 2018-08-08 14:48:54
On 2018-08-08 14:47:24
On 2018-08-08 11:45:46
The content of gas in oil is the percentage of the volume of the oil in which the gas is dissolved in the molecular state. Generally speaking, the dissolved gas is mainly air, so long as there is no bubble occupying a certain geometrical position in the oil, the size of the gas content in the oil does not affect the insulation strength of the oil. However, high gas content will bring some harms, mainly including:
(1) Reduce insulation strength. The solubility of gas in oil has a saturation threshold, and at 25℃ and 1 atmosphere, 10.8% (volume) of air can be dissolved. Therefore, the gas in the oil under certain conditions will exceed the saturation solubility and precipitate out bubbles. Many literatures have introduced that the insulation strength of oil can be reduced by 2/3 due to the presence of air bubbles in the high electric field. When small bubbles attached to the surface of the winding gradually form large bubbles and suddenly float upward, through the high electric field area, partial discharge may be caused, and the oil containing gas will also produce secondary bubbles when partial discharge occurs, further harm insulation, and even flashover.
(2) Accelerate insulation aging. Insulation oil under the action of temperature, if in contact with the oxygen in the air, will occur heat (oxygen) aging. The result of aging is not only water, but also acid and sludge. Sludge deposition on the surface of windings and iron cores will affect the cooling effect and reduce the insulation strength.
(3) Cause the action of gas relay. If the gas content in the oil is high, once the temperature and pressure change, the gas will escape, leading to the gas relay action alarm, and even cause the circuit breaker trip. For example, a certain OSFPSB -- 120,000/220/110/38.5kV main transformer gas relay operation alarm for multiple times is caused by poor sealing of the oil circulation system into the air.
The required value of gas content in oil is stipulated in the Regulations that the gas content of transformer oil in 330 and 500kV operation is generally less than 3% (V/V). Because foreign research shows that when the gas content of oil is less than 3%, the risk of bubbles is very rare.