The quotas of electromagnetic devices such as motors and transformers are usually determined from both mechanical and thermal considerations, and their life is determined by the maximum temperature that can be borne without excessive reduction. Therefore, the life of motor is closely related to its working temperature.
The aging of insulating materials is affected by both time and temperature, so the aging of insulating materials is a chemical phenomenon, which involves slow oxidation and sudden solidification, and causes damage to mechanical durability and dielectric strengtg. In many cases, after considering the aging rate, the life of the insulating material can be expressed as the following exponential function:
Life = AeB/T………(1)
Formula(1) in which A and B are constans and T is the absolute working temperature. According to the past experience, the failure time of the organic insulating materials can be shortened by half when the temperature rises from 8 C°to 14 C°, so the relationship between life and temperature can be obtained.
Insulation life test, it is generally necessary to simulate working conditions as much as possible. These conditions usually include: (1) Heat stock caused by heating to test temperature;
(2) Continuous heating at this temperature; (3) A thermal shock caused by cooling to room temperature or lower; (4) Vibration and mechanical stress that may be encountered in actual work;
(5) Exposure to wet conditions; (6) Dielectric test to determine the state of insulation.