Variable Frequency Motor: Why Are Separate Cooling Fans Fitted For Them?

In industrial variable-frequency speed regulation systems, installing a separate cooling fan for a variable frequency motor is a key measure to ensure stable equipment operation and extend motor service life. Its core purpose is to solve the industry pain point of insufficient low-speed heat dissipation of conventional self-ventilated motors.

 

The cooling fan of a standard ordinary motor is coupled coaxially with the rotor. The fan speed fully follows changes in motor speed, and heat dissipation is realized by the rotating motor driving the fan. This cooling method can meet heat dissipation requirements when the motor runs at rated or medium-high speed, yet it is not suitable for the complex working conditions of variable frequency speed regulation.

 

The core advantage of variable frequency motor lies in wide-range speed regulation. Many industrial production scenarios require the motor to operate at low frequency and low speed for a long time, or to output constant torque under low-speed conditions.

 

When the motor runs at low speed, the speed of the built-in coaxial fan drops significantly synchronously, air volume decreases sharply, and heat dissipation capacity deteriorates greatly.

For constant-torque load equipment such as conveyors, mixers and winches, the operating current will not decrease at low speed. The motor windings continuously generate a large amount of heat, leading to a serious imbalance between heat generation and heat dissipation. It is very likely to cause excessive winding temperature and accelerated aging of insulation layers. Long-term operation will result in overheating, tripping or even direct burnout of the motor, seriously disrupting production continuity.

 

Separate fans are powered by an independent power supply; their operating status is completely decoupled from motor speed. They can deliver constant air volume continuously and provide forced air cooling for the motor across the full speed range, fundamentally resolving the weakness of low-speed heat dissipation.

 

Apart from long-duration low-speed constant-torque working conditions, scenarios with frequent forward/reverse rotation and short-time overload operation also heavily rely on separate fans.

 

Under such working conditions, motor speed fluctuates frequently, and heat dissipation from the built-in fan is highly unstable. Combined with extra heat generated by overload, the motor faces an extremely high risk of overheating. The separate fan enables stable heat dissipation throughout operation and effectively eliminates potential faults.

 

From the perspective of engineering application, the national standard defines conventional coaxial fan cooling as IC411 self-ventilation, while separate fan cooling is designated IC416 forced ventilation.

 

Variable frequency motor equipped with separate fans can maintain rated torque output at low speed without derating, offering stronger adaptability. Some models support delayed air supply after shutdown to fully remove residual heat after equipment stop, providing all-round protection for the motor.

 

Naturally, separate fans are not without drawbacks. After installation, they raise equipment procurement and wiring costs. The added fan assembly also becomes an additional failure point of the equipment, requiring matching overload protection devices. Meanwhile, they produce slight noise and power consumption and occupy certain installation space.

 

For applications with speed regulation only in the medium-high speed range, such as pumps and fans with variable-torque loads, the load and heat generation reduce synchronously when speed drops. In such cases, separate cooling fans are not required.