5. At what frequency does the motor need an external fan?

The ideal control range of electric motors operated by frequency converters is 5–60 Hz, with a constant nominal torque. If the three-phase motor is operated below 30 Hz for a longer period of time, the self-cooling provided by the motor fan is not sufficient and the drive overheats. To avoid this, an external fan is required for cooling. These are available in 230 V, 400 V or as a multivoltage version. This universal fan is often used. It has a normal connection for 400V. In 1-phase operation, the motor of the external fan is operated with a capacitor in a Steinmetz circuit.