Specifications

continue to burn. This is due to its chlorine compound. This makes it an ideal construction and

cable material. The incineration (burning) of PVC causes the release of toxic chemicals like

dioxins and other chemicals that are harmful to humans.

Thermosetting Plastics

Aminos

[a] Urea formaldehyde resins : They are derived from the reaction of urea with formal -

dehyde or its polymers. These resins cannot offer high resistance to heat.

[b] Melamines: When the resin is used with asbestos or glass fibre as filler material, its

heat resistance is in the range of 200

C. It is highly resistant to chemicals. Possess

outstanding electric arc resistance. Excellent resistance to water. Available in full range

of transluscent or opaque colours. Boards are made from these material are used as

distributor heads, casings for electric devices, terminal boards.

Phenolics [Phenol formaldehyde resin]: They are made by a reaction between phenol and

formaldehyde. They are probably the most widely used and cheapest of thermosetting plastics.

Strong, rigid and dimensionally stable.

Heat and solvent resistant. Non-conductors of electricity. Used as Electrical appliance

handles, TV and Radio cabinets

1.9 INSULATING VARNISHES:

Varnish coating, also called Secondary Insulation, is an important component of the insulation

system of an electrical machine. Varnishes, of different types are used in the insulation system

of electrical machines for impregnation and finishing applications. Advantages of these coatings

are:

 Increased mechanical bonding to the winding wires

 Improved dielectric properties

 Improved thermal conductivity

 Protection to the winding against moisture and chemically corrosive environment.

Varnishes are classified based on: 1. Applications of varnish. 2. Type of (varnish) curing

method. 3. Based on main raw material used in varnish.

Insulating varnish based on applications:

1. Impregnating varnish 2. Finishing varnishes 3. Core plate varnishes

4. Bonding varnishes 5. Special purpose varnishes

Insulating varnish based onCuring method :

1. Air drying type 2. Oven baking type

Main raw material used: Alkyd Phenolic, Alkyd, Polyurethane, Isophthalic Alkyd, Modified

polyester, Epoxyester Melamine, Polyestermide, Epoxy, Phenolic, Phenolic Melamine - based.

The above varnishes come in Solvent based and Solvent-less based.