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Explain vacuum impregnation method used for Re-varnishing of insulation with neat diagram.
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Figure of process of vaccum impregnation:- 


Explain the process of vacuum impregnation:- The plant consists of: 1. A large air tight chamber (VIC) i.e. processing or impregnation chamber. 2. The varnish is stored in Tank (VT) i.e. varnish storage tank. 3. Electric heater (H) i.e. preheater. 4. Pump for transfer of varnish from VT to VIC 5. The compressor can create vacuum or pressure in processing chamber when required. 6. Curing tank with electric heater

Procedure for Vacuum Pressure Impregnation (VPI) of the winding:- Step 1:- Perfectly clean the surfaces of all coils windings it should be free from dirt, dust and oily matters etc. Step 2:- Coil / winding should be free from moisture. For the moisture removal heat the winding with the help of high wattage lamp or in an oven till all moisture get evaporated. Step 3:- A pre dried winding is placed into a processing chamber. Step 4:- A vacuum is created in the processing chamber to remove all air, including air within the pores (Air gaps) of the winding.(this is called dry vacuum) Step 5:- Then Varnish is transferred from storage tank to the processing chamber till the entire job is submerged. Step 6:- Again for another time vacuum is created in the processing chamber (this is called wet vacuum.) Step 7:- After that vacuum is released and desired pressure is applied into the processing tank above the varnish level using compressed dry air/nitrogen for better penetration of the varnish resin in to the air pockets of winding and this is maintained for a stipulated time. Step 8:- After desired amount of time, the pressure is released and the varnish is drained back into the varnish storage tank.  Step 9:- The coil (Job) is then taken out from processing chamber and kept on an iron grill tray to drain out excess varnish. Step 10:- Then coil is applies additional coating of finishing gel by brushing or spraying to job for additional protection against moisture, chemical fumes and dust. Step 11:- It is then kept in a electric baking oven till it gets set properly and become dry (i.e. completely cured)curing temperature varies from 90°C to 110°C for 10-20 minutes in some cases one to two hours.

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