3.1.17 When is an external fan used with a geared motor with inverter?

Since a standard electric motor is cooled by its own mechanical fan, this self-cooling cannot be reduced arbitrarily. The guideline for this is 30 Hertz. If the frequency is undershot by the frequency converter control, an external fan must be used for cooling. This guideline applies to drives operating in mode S9, i.e., operation with non-periodic load and speed changes.