- 2076 Asoj · 5 marks
Insulating materials for different machines
Short answer
Electrical insulators are materials with very high resistivity (10^9–10^20 Ωm) and high dielectric strength, used to separate parts at different potentials. Transformers use kraft paper, pressboard and oil; induction motors use enameled wire, Nomex/DMD slot liners and varnish; HV machines use mica tape; DC machines use mica between commutator segments and enamel/glass covering; cables use PVC or XLPE.
What is electrical insulator? Write the various insulating materials used for different kinds of electrical machines?
An electrical insulator is a material of very high resistivity (about to m) and high dielectric strength. It does not allow appreciable current to flow through it, and is used to separate parts at different potentials.
Insulating materials used in different machines
| Machine / part | Insulating materials |
|---|---|
| Transformers | Kraft/manila paper on conductors; pressboard (presspahn) cylinders, barriers and spacers; mineral transformer oil (insulation and coolant); porcelain or epoxy bushings; varnish/carlite on laminations. Dry-type: Nomex, glass, epoxy cast resin |
| Induction motors (LV) | Enamelled copper wire (polyester, polyesterimide); slot liners of Nomex, polyester film or DMD laminate; wedges of fibre or glass laminate; polyester/epoxy varnish impregnation (class B or F) |
| HV motors and alternators | Mica tape with epoxy resin (resin-rich or vacuum pressure impregnated); glass tape; semiconducting slot armour (anti-corona); hydrogen gas cooling in large turbo-alternators |
| DC machines | Enamelled or cotton/glass-covered conductors; mica (micanite) between commutator segments and V-rings; varnished cloth and paper for field coils; shellac and varnish impregnation |
| Small/fractional motors and appliances | Enamelled wire, paper, PVC, fibre sheet; class A or E |
| Traction and high-temperature machines | Class H materials: glass, mica, silicone resins, polyimide (Kapton) |
| Cables and leads | PVC, XLPE, rubber, silicone rubber |
General groups
- Solid: mica, paper, cotton, glass fibre, porcelain, rubber, plastics, resins and varnishes.
- Liquid: mineral oil, silicone fluid, ester oils.
- Gas: air, hydrogen, nitrogen, SF₆.
The insulation must be chosen for its thermal class (Y 90, A 105, E 120, B 130, F 155, H 180, C >180 °C). Its life depends mainly on the operating temperature.
✓ Answer checked by Claude Sonnet 5.5
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