 | Electrical Machines - Basic vocational knowledge (Institut für Berufliche Entwicklung, 144 p.) |
 |  | 3. Execution of rotating electrical machines |
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3.6. Heat resistance categories
The functional life of machine windings depends to a great extent on the thermal strain of insulations. Constant temperature must, moreover, be so limited as to prevent heating up over a longer period leading to an impairment of electrical and mechanical properties.
Survey 12 - Insulation classes
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IC Highest permissible permanent temperature (celsius) |
Short characterization of the main categories of insulating materials | |
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Y |
90 |
non-impregnated insulation materials of cellulose fibres or silks; forming materials on the basis of urea formaldehyde resin |
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A |
105 |
impregnated as insulation or in liquid insulating materials such as oil - trenched insulation materials of cellulose fibres or silks; forming materials on the basis of melamine formaldehyde resin |
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E |
120 |
cellulose fibres or silks with synthetic lacquers as coating means; laminated plastics on phenolic resin basis; forming materials on the basis of phenol, aminotriazine and polyester resins |
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B |
130 |
insulating materials on the basis of mica, asbestos, glass silk or terephthalic acid polyester with organic binding and trenching agents |
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F |
155 |
insulating materials on the basis of mica, asbestos or glass silk with synthetic binding or trenching agents |
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180 |
insulating materials on the basis of silicone elastomers and on the basis of mica, asbestos or glass silk with silicium-organic binding or trenching agents |
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C |
over 180 |
mica, glass, quartz or ceramic insulating materials with or without inorganic binding agents |
Exceeding the highest permissible constant temperature in line with heat resistance categories significantly decreases the service life of the machine. For example, a motor can only withstand 50 per cent overloading for about two minutes.
A heat resistance category denotes a category to which an insulating material has been allocated in regard to its highest tolerable constant temperature.
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