INSULATING VARNISHES

INSULATING VARNISHES

Unknown   22:49   No comments:

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

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.

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CHARACTERISTICS OF A GOOD INSULATING MATERIAL

CHARACTERISTICS OF A GOOD INSULATING MATERIAL

Unknown   22:40   No comments:

CHARACTERISTICS OF A GOOD INSULATING MATERIAL

A good insulating material should possess the following characteristics.

I. Very high insulation resistance.
II. High dielectric strength.
III. Low thermal expansion.
IV. Non-inflammable when exposed to arcing.
V. Resistant to oils or liquids, gas fumes, acids and alkalies.
VI. Should have no deteriorating effect on the material, in contact with it.
VII.Good thermal conductivity.
VIII.High mechanical strength
IX. High thermal strength.
X. Should be resistant to thermal and chemical deterioration.
XI. Should be resistant to moisture absorption.

THERE ARE FOUR PRINCIPAL AREAS WHERE INSULATION

MUST BE APPLIED. They are

a) between conductor /coils and earth (phase-to-earth),

b) between conductor /coils of different phases (phase-to-phase),

c) between turns in a coil (inter-turn) and

d) between the coils of the same phase (inter-coil)

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CLASSIFICATION OF INSULATING MATERIALS

CLASSIFICATION OF INSULATING MATERIALS

Unknown   00:49   No comments:

CLASSIFICATION OF INSULATING MATERIALS

1. Classification according to substances and materials.

2. Classification according to temperature.

Classification according to substances and materials :

(i) Solid Insulating Materials [Inorganic and organic] Mica, wood, slate, glass, porcelain, rubber, cotton, silk, rayon, terylene, paper and cellulose materials etc.

(ii) Liquid Insulating Materials [Oils and Varnishes] Refined hydrocarbon minerals oils, Linseed oil, spirit and synthetic varnishes, etc.

(iii) Gaseous Insulating Materials Dry air, carbon dioxide, argon, nitrogen, etc.

Classification according to temperature 
The insulating materials are classified mainly based on the thermal limit. The performance of the insulation depends on its operating temperature. The higher the temperature, the higher will be the rate of its chemical degrading, and hence the lower will be its useful life as shown in figure. If a reasonably long life of insulation is expected, its operating temperature must be maintained low. Therefore, it is necessary to determine the limits of temperature for the insulation, which will ensure safe operation over its expected life.

Thus the insulating materials are grouped into different classes Y, A, B, and C with
temperature limits of 90 ⁰C, 105⁰C and 130⁰C for the first three classes and no specific limit

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