The Role and Control of Fans in Electric Motor Cooling Systems

The Role and Control of Fans in Electric Motor Cooling Systems:

Fans play a crucial role in the ventilation and cooling systems of electric motors. They serve as essential pressure components, compensating for pressure losses incurred as cooling mediums pass through the ventilation paths. Fans deliver a consistent flow of cooling medium to the heat-generating components of the motor, carrying heat away and transferring it to the next cooling stage.

In general, fans installed inside the motor cavity are referred to as internal fans, while those mounted outside the motor housing are called external fans. Both types are fixed to the rotor and rotate with it. For small and medium-sized motors, cooling primarily relies on the airflow pressure generated by external fans. This air, guided by a fan cover, flows over the motor housing surface, dissipating the heat generated by the motor into the surrounding environment. Typically, an external fan is installed at the non-drive end of the motor, forming an external ventilation and cooling system in conjunction with the fan cover and housing fins. This system ensures a stable temperature gradient from the internal heat source to the motor housing and then to the ambient environment, preventing the internal temperature from exceeding the design limits.

It is essential to match the motor fan with the intake area and maximum diameter of the fan cover. For high-efficiency motors, optimizing the shape and dimensions of ventilation paths between the fan cover and the motor's external surface minimizes air friction while achieving superior cooling performance.

For medium and large motors, the internal ventilation structure is more complex, often causing localized heat accumulation. To address this, many motors incorporate axial and radial ventilation channels in the core, with internal fans mounted at one or both ends of the rotor. These fans create an independent air circulation system, ensuring efficient cooling. Dual internal fans suit motors with radial ventilation structures, while single internal fans are used in motors with axial or hybrid ventilation designs.

As a key pressure component of the cooling system, the fan works with the motor core and windings to drive the internal cooling medium along predetermined paths, forming a standalone cooling system. For instance, in radial ventilation structures, the motor core consists of at least three core sections, with ventilation slots between adjacent sections. The airflow resistance of these slots increases gradually from the motor ends to the center, balancing the airflow across multiple channels. This design achieves a uniform temperature distribution along the motor's axial direction, effectively reducing the highest temperature in the system and preventing overheating failures.

Axial ventilation can be classified into full or partial axial flow. In this design, cooling air enters axial holes in the core laminations from one end and exits from the other, or it flows in from both ends and is discharged through radial ducts in the middle. Selecting the appropriate design based on the motor's internal structure is key to reducing temperature rise and improving the motor's technical and economic performance.

Rotor-mounted fans are suitable only for motors running at constant frequency. For variable-frequency motors, significant speed variations—especially at low speeds—render rotor-mounted fans inadequate for cooling. In such cases, standalone fans are installed to ensure proper heat dissipation under varying operating conditions.