Electrical machines are primarily classified into two groups. Electrical motors and Electrical Generators. Motors are the electrical machines that convert electrical energy to mechanical energy and generators are the machines that convert mechanical energy to electrical energy. An electric machine is made of various types of materials. There are three major constituents found in any electrical machine: Insulation materials, Magnetic materials, and conductive and resistive components.
Insulation materials are non-metallic materials that serve to provide thermal insulation, galvanic separation and provide the overall appearance to machines. Good insulation materials should possess:
- Appropriate mechanical strength to suite the application
- Chemical attacks should have minimum to negligible impact on materials
- It should confine electric current in definitive regions
- It should have high dielectric strength over all temperature ranges
- It should operate properly within defined temperature range
- It should possess high melting
- It should possess high resistance
- Liquid – no evaporation or volatilization.
- Low dissipation factor (loss target),
- No deterioration should happen even in case of repeated heat cycle
- The dielectric hysteresis should be low
- The dielectric loss angle should be low
- The material should be able to withstand high temperatures
- The material should be free from moisture and ionic contamination contents
- The material should have good machinability for mass production
- The material should have good thermal conductivity
- The permittivity of material should be low
- The thermal stability of material should be high
- The material should possess ability to withstand:
Magnetic materials used in electrical machines are classified on the relative permeability. On a broad scale, three classes of magnetic materials exists. That includes:
- Diamagnetic materials: Diamagnetic materials possess small relative permeability. Materials whose relative permeability is less than or equal to 1. μn ≤ 1. Examples include copper, silver, and gold. Diamagnetic materials have linear B-H curve.
- Paramagnetic materials: The relative permeability of paramagnetic materials is slightly greater than or equal to one. μn ≥ 1. Examples include Platinum and tungsten. Air is also a paramagnetic material. Just like diamagnetic materials, the paramagnetic materials have linear B-H curve.
- Ferromagnetic materials: These materials have the relative permeability that largely exceeds 1. μn >> 1. The B-H curve of ferromagnetic materials is nonlinear.
Resistive materials used in reference to electrical machines are electrical components such as starters, regulators, rheostats.