Vacuum Pressure Impregnation System

Vacuum Pressure Impregnation

Vacuum pressure impregnation or VPI is process of sealing porous material with resin & it perform to order function of improve insulation system.VPI system is primarily used in electrical engineering, aviation & automobile industries. For our purpose is to here we discuss impregnation process for electrical machines such as motor and generators.

·       Why do we need VPI system?

This give protection against dust, moisture, fungi & reasonable resistance to acid-alkali fumes. The first & main cause of the failure of electrical machine due to breakdown of insulation used in core & winding. As insulation ages the breakdown voltage machines begins consider substantially therefore robust insulation system is necessary. If the gaps are available in core or winding coil then this cause of issues related to temperature & efficiency. Gaps & voids provides low resistance path for electric charges. Thus lowering the breakdown voltages in insulation systems. Partial discharge is make causing progressive deterioration of insulating material. It possible to electrical breakdown & failure during high voltage test. There is also problem of structural stability. This gap weak the material. Therefore it is chance to break or cut the material under pressure (electric or magnetic stress) or vibration. Untreated insulation results negatively affect thermoconductivity & increase internal temperature rises of machines. Impregnation with varnish severs to protect the stator winding against vibration effect, provide additional insulation & also improve heat conduction.

    

·       What methods are available for impregnation?

There are various impregnation methods are available. The impregnation method choose by considering voltage of machine and cost of the system. For example: Many low voltage manufacturers using hot dipping technology. However for our purpose is we will be discuss the method of Vacuum Pressure Impregnation or VPI. Which involved the use of vacuum & pressure as implies along with resin instead of traditional varnish. It permanently use for low & high voltage motor & generators.

·       What are steps for VPI?

Vacuum Pressure Impregnation consist of following steps:

1.     Pre-heat: First the part (Stack with winding & rotor) place in oven & pre-heated in order to evaporated any moisture & improve resin penetration.

2.      Dry Vacuum: Dry Vacuum is then apply to remove air & any remaining moisture.

3.     Filling: The resign introduce into the chamber from the bottom off & fill in gaps in material.

4.     Wet Vacuum: Vacuum is reduce intercepted for certain amount of time. 

5.     Pressure: Through the use of dry air (Nitrogen) or other gases pressure is applied to the chamber to further increase penetration.

6.     Draining: Finally the chamber pressure is reduce & chamber is drain by shifting the resin to other tank .Then Part or job is removed.

7.     Curing: Part or job place in the over for heat up the resin.  

·       What are the part or units of vacuum impregnation plant?

1. Impregnation tank                                          

2. Varnish or resin storage tank

3. Vacuum system

4. Varnish or resin circulating system

5. Hydraulic system

6. Pneumatic system

7. Cooling water pipeline system

8. Measuring & control system