Induction machines rely on a relatively simple yet robust construction, considering that their durability can vary according to the durability of the insulation of the winding, and can be varied by factors such as possible vibrations, humidity and corrosive environments. Among these factors, the most significant is the temperature supported by the insulating materials used. Experience has shown that insulation has an almost unlimited duration if its temperature is kept below the limit of its thermal class. Above this limit, the insulation durability becomes shorter as the working temperature gets higher.
The increase of about ten degrees above the thermal class limit of the insulation temperature, allows the winding durability to decrease by half. For longer durability, the use of thermal sensors is recommended for retention of the winding. The decrease in engine durability does not refer to high temperatures, when the insulation burns out and the winding is destroyed. The durability of the insulation refers to the gradual aging of the insulation, which over time becomes dry, losing its insulating action until it can no longer withstand the applied voltage and results in a short circuit. https://www.mrosupply.com/ac-motors/hvac-motors/26551_rm3115_baldor/