High speed electric motors must solve six issues,the first of which is the hot.

The motor loss increases with the geometric progression of the speed, and the heat generated by high loss causes the motor temperature to rise rapidly. To maintain high-speed operation, it is necessary to design a cooling method with good heat dissipation. We can see that the common cooling methods for high-speed motors are:
1. “Internal forced air cooling” is shown in the figure below. Strong cold air can directly blow into the motor to take away the heat on the winding and iron core. This method generally occurs in situations where strong wind is already available, such as air compressors, blowers, and aircraft motors.
2. In applications where motors must be enclosed for protection or without strong winds, the most commonly used method is internal oil cooling, such as the combination of stator slot oil cooling used in AVL designed high-speed motors. Some motors also use a combination of winding oil spray cooling, stator oil cooling, rotor oil cooling, and other methods.