Electric Insulation System
Insulation Class
| Class | Limiting Temprature |
| Y | 90 oC |
| A | 105o C |
| E | 120o C |
| B | 130o C |
| F | 155o C |
| H | 180o C |
| 200 | 200o C |
| 220 | 220o C |
| 250 | 250o C |
Electric insulation system has to withstand variety of stresses during the operation of electrical machines these stresses must be taken into consideration before selecting the correct insulating materials.
1. Mechanical Stress
It arises due to moving parts in the electrical machines, centrifugal forces, vibration and as a result of fluctuating temprature in winding with changes in load.2. Electrical Stress
It comes in to play due to electrical field generated, dielectric breakdown, corona discharges, arcing with ground or between phases.3. Thermal Stress
This is produced because of losses in conductor, stampings and insulations defects. Generally insulating materials are poor conductor of heat which aggravates the problem further.4. Enviromental Stress
Exposure to humidity (moisture), radiation+, oxidation^, ozone, salinity chemical fumes are some of the reasons for enviormental stress.+ Nuclear power plants
^ Refrigeration motor has to withstand CFC attackBeside above stresses insulation material should withstand the demands of processing arising during the manufacture of electrical machine. Deterioration in insulation system is generally caused by combination of several factors playing simultaneously. While making the choice of a correct insulating material following factors should be considered.
| Physical | Thermal | Electrical | Chemical |
| Tensile Strength | Thermal Class | Dielectrical Strength | Water absorption |
| Elongation | Softening Point | Insulation Resistance | Resistance to hydrolysis |
| Compressive Strength | Heat Deflection temp. | Arc Resistance | Resin Adhesion |
| Trearing Strength | Thermal Conductivity | Current Resistance | Ability to withstand specific chemical/radiation attack |
| Cross Breaking Strength | Short duration high termal load | Surface Discharges | Resistance to solvent |
| Foldting Capacity | Dissipation Loss | Impregnating Capacity | |
| Flexibility | Dielectric Constant | Curing Characteristics | |
| Spring Elasticity | Compatiability | ||
| Punchabity | |||
| Scratch resistance | |||
| Hardness | |||
| Surface Property | |||
| Viscosity | |||
| Specific Gravity |
Basic Materials
Resins Varnishes Enamels |
Alkyd, Amino, Unsaturated Polyester, Epoxy, Polyamide, Polyamide imide, Polyimide, Silicone Polyphenyl Sulfide, PTFE, Acrylics, Polyurethane, Polyesterimide |
| Papers, Nonwovens, Films & Fabrics | Celluose paper, Aramid paper, Mica Paper, Ceramic Paper, Polyester Fleece, Aramid Fleece, Polyester Film, Polypropylene Film, Polycarbonate Film, Polythene Film, Polyvinyl Chloride film, PBT film, PVDF film, PEI, PEEK, Polyimide Film, Fibreglass Fabric, Polyester fabric, Carbon fibre fabric, Aramid fabric. |
| Elastomers | Natural Rubber, Polybutadiene, ABS, Polyisobutylene, Neoprene, Butyl Rubber, Silicone FluroElastomer. |
Electrical insulating materials are characterised by following
1)High dielectric strength.
2)Low dielectric constant.
3)Low dielectric loss(tan delta).
4)High volume and surface resistivity ,insulation resistance.
5)High tracking , corona & arc resistance.
