Insulation system
Characterizes an Insulation or insulating materials specified (eg Insulating of enamelled copper wire, the slot insulation of electric motors or the layer insulation of transformers ) with respect to their maximum use temperature. In electrical components, high temperatures can occur which impair or destroy the insulation. The insulating materials are classified with different limit temperatures according to their heat resistance to thermal classes. This must not be exceeded permanently in operation. The values must be below the melting point or decomposition temperature are, however, also be low enough to preclude failure due to thermal aging during the life of the component.
The insulation classes are defined in DIN EN 60085:
The classes refer to both individual electrical insulating materials (EIM ), as well as electrical insulation systems (EIS ), which are composed of multiple materials. An insulation system and the materials from which it is made must not have necessarily the same insulation class. For example, a material may exhibit the protective effect of a substance such as resin encasing a class higher than without wrapping.
The insulant should not be considered as a typical characteristic material values , but rather as reference values . Basically, the properties of an insulating material to deteriorate with increasing temperature, for example, because the softening temperature is exceeded. Furthermore, the material aging under the influence of temperature, that is, the properties decrease with time further. The aging rate is determined by the Arrhenius' equation by the temperature. Therefore, the assignment of a material or system always depend on
The same material or system can therefore fulfill different insulation classes for different applications. The classification must be done with proven insulating materials on the basis of operational experience and comparative tests. The exact requirements and operating temperatures have been resolved in the individual product standards. So an average winding temperature of 120 ° C, for example, for a dry transformer insulation rating allowed 155 (F) in nominal operation. The temperature in the hottest point of the winding may be in the rated maximum operating 145 ° C, short term up to 180 ° C.
In electric motors for industrial use, the classes F and H are common.
Thermal switch, thermal fuses and motor protection switch of a motor or transformer to ensure that the temperature limits are not exceeded.