Why the insulation temperature of different insulation materials will be different?

For different grades of diamond dotted paper, the ultimate operating temperature will be different. Therefore, in many electrical installation, also need to take into account the entire circuit can withstand the maximum temperature conditions. When there are special circumstances, some important materials can withstand high temperatures, but also to measure the stability of the entire electrical device key. For the insulation of several common insulation class, like the A-class limit operating temperature of 105 ℃, but its maximum allowable temperature is only 90 ℃. The reason why these two temperature values ​​will be different, mainly due to the following reasons:
    1, thermometer method. The measurement results reflect the local surface temperature of the winding insulation. This number is averaged about 15 ° C lower than the actual maximum temperature of the winding insulation, the "hottest". The law is the simplest, in the medium and small motor field application of the most extensive. For low-resistance windings, this method is more accurate than the resistance method. As the mercury thermometer in the alternating magnetic field due to eddy current loss heat, so the use of alcohol in the AC motor thermometer.
    2, resistance method. The measurement results reflect the average value of the entire winding copper temperature. The number of the actual maximum temperature according to the different phenolic laminated sheet level reduced by 5 ~ 15 ℃. The method is to measure the cold and thermal resistance of the conductor, according to the formula to calculate the average temperature rise.
    3, embedded detection thermometer test copper or platinum resistance thermometer or thermocouple embedded in the winding, the core or other needs to measure the expected temperature of the highest parts. The measurement results reflect the temperature at which the temperature measurement element contacts. Large motors often use this method to monitor the operating temperature of the motor. In the range of 100 ~ 200 ℃ copper or platinum resistance thermometer is more accurate, and thermocouple is not commonly used.
    In addition, the closed fan cooling motor resistance method measured by the temperature measured by the thermometer method of 0 ~ 15% higher; protection of 10% to 20%. While the resistance method and the embedded copper resistance thermometer difference of ± 5%. Therefore, the various measured methods measured by the temperature and the actual maximum temperature difference, and can not really reflect the flexible composite materials of insulating materials, so the insulation material should be "limit the operating temperature" minus the difference is "Maximum allowable operating temperature".