Atmospheric drying is carried out for transformers with a working voltage of 33kv. In higher voltage class transformers thicker and longer insulation parts are used. Ordinary air drying will not be able to remove moisture contained in this insulation within a reasonable time. Therefore vacuum drying is used for such transformers. Vacuum drying also accelerates the drying speed.

at normal atmospheric pressure boiling point of water is 100 deg c. But in vacuum water boils at very low temperatures. Following details are given to get an idea of relation between pressure and boiling point of water.

pressure boiling point
760mm/hg 100 deg c
4mm/hg 1. 24 deg c
1mm/hg -19 deg c

vacuum drying autoclave

simply placing transformer in autoclave vessel under vacuum will not remove moisture form that. For evaporating water into steam latent heat of water is to be supplied.

when transformer put in to the autoclave for drying heat energy is transferred to transformer via convection and radiation. Compared to convection energy transfer by radiation is very low. During vacuum drying as air is sucked out there will not be any transfer of heat by convection. This necessitates heating by hot air of sufficient duration,before vacuum drying in the autoclave vessel by externally either by thermic fluid heating system/electric heating system/steam heating by means of radiator coils inside autoclave or limpets welded outside the autoclave..

Atmospheric drying is carried out for transformers with a working voltage of 33kv. In higher voltage class transformers thicker and longer insulation parts are used. Ordinary air drying will not be able to remove moisture contained in this insulation within a reasonable time. Therefore vacuum drying is used for such transformers. Vacuum drying also accelerates the drying speed.

at normal atmospheric pressure boiling point of water is 100 deg c. But in vacuum water boils at very low temperatures. Following details are given to get an idea of relation between pressure and boiling point of water.

pressure boiling point
760mm/hg 100 deg c
4mm/hg 1. 24 deg c
1mm/hg -19 deg c

vacuum drying autoclave

simply placing transformer in autoclave vessel under vacuum will not remove moisture form that. For evaporating water into steam latent heat of water is to be supplied.

when transformer put in to the autoclave for drying heat energy is transferred to transformer via convection and radiation. Compared to convection energy transfer by radiation is very low. During vacuum drying as air is sucked out there will not be any transfer of heat by convection. This necessitates heating by hot air of sufficient duration,before vacuum drying in the autoclave vessel by externally either by thermic fluid heating system/electric heating system/steam heating by means of radiator coils inside autoclave or limpets welded outside the autoclave..