The use of electrical insulation products to a variety of factors (such as temperature, electrical and mechanical stress, vibration, harmful gases, chemicals, moisture, dust, and irradiation, etc.) effects, and the temperature usually is the aging of insulation materials and dominant factor. A practical result has been recognized worldwide as the heat resistance classification method, that is, the heat resistance of the electrical insulation is divided into several heat levels. Motor insulation class depends on its use of heat insulating material grades. The insulating material under normal conditions in accordance with the allowable limit temperature can be divided into Y, A, E, B, F, C, H seven levels, the limit temperatures of Y ≤ 90 °, A ≤ 105 °, E ≤ 120 °, B ≤ 130 °, F ≤ 155 °, H ≤ 180 °, C> 180 °.