Forced ventilation
By forced ventilation an is electric motor cooled by an external device. These devices are also known as external fans or external ventilation units .
Electric motors of simple design cool themselves on their surface through passive heat exchange with the ambient air. For this purpose, the motor housing is usually provided with cooling fins, which enlarge the surface and thus improve the heat exchange.
Highly loaded motors also supply cooling air via a radial fan wheel . This is mounted on the stub shaft opposite the force-emitting side. It rotates according to the engine speed . The air flow is directed over the motor housing through a fan cover.
In modern drives, electric motors are often controlled with variable speed via frequency converters, i. H. the motors must deliver high performance even at very low speeds. Self-cooling via its own fan wheel, which runs synchronously , is no longer sufficient at such low speeds. The engine would be overloaded and would have to be more powerful as a result, so it would be more expensive and larger.
Forced ventilation provides a remedy for this problem. It consists of a fan cover with a fan with its own drive that is completely independent of the motor to be cooled. This requires its own power supply, but thus provides a permanent air flow to cool the motor sufficiently under all operating conditions. Depending on the design, axial fans or centrifugal fans are used in external ventilation.
literature
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
- Gregor D. Häberle, Heinz O. Häberle: Transformers and electrical machines in power engineering systems. 2nd edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 1990, ISBN 3-8085-5002-3
