In the process of vacuum drying of electrical products, such as transformers, transformers, capacitors, etc., it is required that the vacuum system can pump out a large number of water vapor and solvents in a certain pressure range, and at the end of drying, it must reach a lower limit pressure.
For example, for a medium-sized transformer, the moisture content of the insulating material is as high as 400-500kg, and the whole drying cycle is 70h. Under the inlet pressure of 45mbar, the vacuum system is required to pump 90% – 95% of the moisture content within 48h, that is, the capacity of pumping steam per hour is about 15kg, and it still recovers to the original limit pressure of 10-2mbar after drying.
Steam treatment unit principle
In the vacuum state, when the temperature of water or steam is higher than the boiling point, they enter the pump cavity in the state of gas.
The slide valve vacuum pump itself is a heating source, and the liquid ring vacuum pump provides a low pressure for the separator of the slide valve vacuum pump, so the water or other steam discharged to the separator is also in a vacuum state, and the temperature is high enough to keep them in a gas state, and any tiny liquid drop will be evaporated in the separator.
The water or other steam discharged to the liquid ring vacuum pump, due to the relatively low temperature in the liquid ring vacuum pump, are condensed and become part of the sealing liquid.
In order to prevent the steam from being condensed in the pump, the oil temperature of the vacuum pump must be high enough, generally set in the range of 60-75, and the oil temperature higher than 80 will cause the vacuum pump oil to be oxidized. The required oil temperature can be controlled by automatically adjusting the cooling water entering the slide valve vacuum pump.
Adjusting the pressure in the spool pump separator
If the slide valve pump works at 65 when dealing with water vapor, the vacuum overflow valve installed on the exhaust pipe of the slide valve vacuum pump shall be set at 15000-20000 PA, which is lower than the saturated steam pressure of water at 65.
Oil pump pressure
In order to operate the oil pump normally under vacuum, the oil pressure must be kept at 0.2-0.4 MPa and the oil supply shall be continuous.
Experiment of removing water vapor
Steam treatment device in vacuum system advantage
1. It can deal with a large number of condensable gas or volatile gas.
2. The extracted steam will not be condensed in the pump, reducing the corrosion to the metal surface.
3. The oil pollution is avoided, the number of oil changes is greatly reduced, and the operation cost is significantly reduced.
4. The performance degradation caused by oil pollution is eliminated.
5. It can maintain low working pressure in wet process.