The electric induction motor is a simple and robust construction machine and its durability depends almost exclusively on the durability of the winding insulation. This is altered by many factors such as vibrations, humidity and corrosive environments, among others. Among these factors, the most significant is the temperature supported by the insulating materials used.
The increase of eight to ten degrees above the thermal class limit of the insulation temperature, allows the reduction of the winding durability by half. For longer durability, the use of thermal sensors is recommended for retention of the winding.
At the moment we mention the decrease of the durability of the motor, it is not referring to the high temperatures, when the insulation burns and the winding is suddenly 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.
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. https://www.mrosupply.com/bearings/spherical-roller-bearings/2070315_24138-cck30w33_skf-bearing/