Answer / k.prakashchandra

To dehydrate the windings.In view of high level of water /
moisture content in insulation ,it is recommended to
thoroughly dehydrate the windings by subjecting to vacuum
heating and drying after untanking the oil.Care should be
taken to see that the tank would not buckle due to the vacuum.

Answer / santosh

vaccum creating to check any leakage point.

Answer / byd

Generally Hermetic Onan transnformer vaccume before oil
filteration and after oil filling,, because if there is
any air inside of transformer tank and oil then we
apply anergy after there will be short circuit and
insilation resistances will be min, and IEC 60076-1 High
voltage test, if transformer is 33kv, you should apply
mono phase to HV winding as 70kv for 1 minute,, if there
is any short circuit it means oil didnt vaccume ,, or
there is some insilation wrong ,, i am sorry my english
is not good

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