Impregnating Resins
Application Note: Secondary Insulation
Impregnating Varnishes, Solventless Impregnating Resins and Finishing Compounds
1.0 General
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 India offers a wide range of solvent-borne, waterbased varnishes & solventless resins for various applications.
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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, excess varnish is allowed to drip and cured. In a slight variation to this simple dip process, the predried 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
Predried winding is placed in an impregnant chamber, which is then evacuated 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 breaking vacuum. VPI method is generally employed for electrical machines and coils requiring high quality impregnation.
Trickle Impregnation
In this method, a thin jet of impregnating resin is poured on to preheated & rotating winding, 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.
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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: abhay.kulthe@altana.com
UL Approvals
UL File # | Product | Chemical base | Varnish/ Resin | |
TP (*) | HC(**) | |||
E73288 | Elmotherm H 71 | Alkyd Polyurethane | 180 | 200 |
| Elmotherm FR 63 | Epoxy Ester | 180 | 200 |
| Dobeckan FT 2001/... | Polyester | 180 | 200 |
| Dobeckan FT 1040/... | Unsaturated | 180 | 220 |
| Dobeckan FT 1052/... | Unsaturated | 180 | 220 |
| DobeDockan FT 1080/... | Unsaturated | 180 | 220 |
| Dobeckan FT 2005/... EK | Polyester | 200 | 220 |
E73015 | ISOPOXY 800 | Epoxy | 200 | 200 |
| ISONEL 31J | Modified Polyester | 180 | 180 |
| ISONEL 51J | Modified Polyester | 200 | 220 |
(*) TP = Enamelled wire twisted pair with wire according to (NEMA MW 1000-Part 35)
(**) HC = Helical coil bond strength method