Force ventilated motors-advantages in fixed and variable-speed applications

The traditional design of industrial induction motors uses a radial fan mounted directly on the motor shaft to ensure adequate cooling during operation. This provides the lowest cost, most compact design and simplest construction for most fixed speed applications, where the induction motor dominates all other forms of drive technology. However, there is a growing need with variable speed applications for motors with improved cooling when operating at low speeds. The simplest way to achieve this is to provide a second, small, constant speed induction motor to drive the cooling fan. The use of force ventilated, or separately blown motors is not new, but the advent of static frequency inverters brings new life to the concept. The force ventilated motor offers several advantages when applied in a variable speed drive. The authors highlight these advantages for the benefit of prospective users. There are also some fixed speed applications where the force ventilated motor has an advantage which are also discussed