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close this bookElectrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)
View the documentIntroduction
Open this folder and view contents1. General information about electrical machines
Open this folder and view contents2. Basic principles
close this folder3. Execution of rotating electrical machines
View the document3.1. Size
Open this folder and view contents3.2. Designs
Open this folder and view contents3.3. Degree of protection
Open this folder and view contents3.4. Cooling
Open this folder and view contents3.5. Mode of operation
View the document3.6. Heat resistance categories
Open this folder and view contents3.7. Connection designations of electrical machines
Open this folder and view contents3.8. Rotating electrical machines in rotational sense
View the document3.9. Rating plate
Open this folder and view contents4. Synchronous machines
Open this folder and view contents5. Asynchronous motors
Open this folder and view contents6. Direct current machines
Open this folder and view contents7. Single-phase alternating current motors
Open this folder and view contents8. Transformer
 

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

IC Highest permissible permanent temperature (celsius)

Short characterization of the main categories of insulating materials

Y

90

non-impregnated insulation materials of cellulose fibres or silks; forming materials on the basis of urea formaldehyde resin

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

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

B

130

insulating materials on the basis of mica, asbestos, glass silk or terephthalic acid polyester with organic binding and trenching agents

F

155

insulating materials on the basis of mica, asbestos or glass silk with synthetic binding or trenching agents

 

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

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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