Application Note: Secondary Insulation
Impregnating Varnishes, Solventless Impregnating Resins and Finishing Compounds
Organic varnishes & solventless resins are widely used in the Insulation system of electrical machines for impregnation and finishing applications. Impregnating & finishing agents offer several advantages, such as:
- Increased mechanical bonding to the winding wire
- Improved dielectric properties
- Improved thermal conductivity
- Protection to the winding against moisture & chemically corrosive Environment
ELANTAS Beck offers a wide range of solvent-borne, waterbased varnishes & solventless resins for various applications.
2.0 Application Methods for Impregnation
Depending upon the types & size of winding, production rate, several application methods are adopted during manufacture of electrical machines.
Dip or Flood Impregnation
In this method preheated winding is slowly dipped in the varnish or resin, preferably with the slots in vertical direction. After certain time, the winding is removed from the varnish tank and excess varnish allowed to drip and then cured. In a slight variation to this simple dip process, the pre-dried winding is kept in a varnish tank and varnish pumped to slowly raise the varnish level till the winding is completely submerged. This is called flood impregnation. One of the limitations of this method is that impregnating agent gets coated on unwanted parts of the winding.
Vacuum or Vacuum-Pressure Impregnation (VPI) Method
Pre-dried winding is placed in an impregnating chamber, which is then subjected to very low vacuum. The impregnating agent is fed in till complete submersion of winding. For further penetration in compact or fine size wire wound units, dry compressed air or Nitrogen pressure is applied, after releasing vacuum. VPI method is generally employed for electrical machines and coils requiring high quality impregnation.
In this method, resin is applied by a thin jet of impregnating resin, on preheated & rotating winding which may be sometimes kept inclined to the horizontal axis. The impregnating resin penetrates through the winding and gets polymerized in a short time. The method offers several advantages such as: short processing time, no long post curing, no drain loss, high retention & consistent quality of impregnation.
3.0 Application Methods for Finishing varnishes
Finishing varnishes are used to give an enveloping coat over the exposed impregnated winding for additional protection against moisture, chemical fumes and dust. Finishing varnish or resin is generally applied by brushing, spraying. Depending upon the type used, the winding is cured at ambient or elevated temperature in an oven.
4.0 Application of Special Varnishes
For insulation of core plates, glass-fibre sleeving, fabric, tape or cord, mica paper tapes, etc. specific application methods are employed. Conveyorized coating plants are generally used in which dipping, wiping and curing are done under controlled conditions.
For further details please contact our Technical Services department, E-mail id: abhaey.kkulthe@ altana. com
Use of insulation system is limited to the combinations of insulating materials specified below. Wherever more than one items are specified , they may be used together or they may be alternatives to one another.
Wherever thickness are specified they are minimum.
Optional items are not necessarily required in every design.