Vacuum pump selection problem

Vacuum pump is the key equipment in the process of vacuum drying. The selection of vacuum pump type should consider whether it is suitable for the field production process.
The power transformer drying process is actually a dehumidification process, there is a large amount of water vapor to vent, so the selection of the former pump to be able to withstand the higher partial pressure of water vapor, such as the use of rotary vane pump or water ring pump.
But the general large power transformer (voltage grade 110kV and above) in the drying vacuum tank system the limit vacuum requirements in 1OPa, water ring pump plus a roots booster pump are far from meeting the requirements (let alone consider the system leakage).
Introduced the present domestic equipment and imported by the single-stage rotary vane vacuum pump (with gas ballast valve) can be up to 50 pa limit vacuum (domestic single-stage rotary vane pump can achieve even 10 pa, but performance has certain gap with imported), coupled with the level of roots pump, vacuum degree can be improved at least under 10 pa (considering system leakage rate of pressure rise within l0h no greater than 93 pa).
Therefore, now the transformer vacuum drying equipment tend to choose rotary vane vacuum pump as the front vacuum pump.
At the same time, there is a large amount of water mixed in the pumping medium. According to the saturation vapor pressure curve of water, when the pump temperature reaches 60, the saturation vapor pressure of water can reach 19.8kpa. This partial pressure affects the ultimate vacuum of the pump.
If the use of ballast pump, it can suck water vapor, but its maximum inlet pressure (partial pressure of water vapor) and pump volume and pump temperature.
In the case of a certain degree of vacuum, the higher the temperature, the more volatile water, liquid to the pump oil in the water is very little.
Therefore, operating the vacuum pump at the highest temperature is an effective way to ensure that the vacuum pump can reduce oil emulsification and obtain a high vacuum.
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