On finding compact motor solutions for transient applications

Applications such as emergency breakers, protective devices in explosive environments, emergency exit openings, etc., fall into a broad category that can be grouped under the general term transient applications. There are cases in which a motor is to be operated only for a short duration. The use of standard procedures to select or design a motor for these transient applications, will most probably result in an over dimensioned and an over-sized motor. An alternate approach is hence required. This paper provides guidelines on how to select an off-the-shelf motor and when necessary, on how to design a new motor for such applications. A design example is also provided, and the analysis is verified by building and testing a prototype. It is found that with some derating calculations, an off-the-shelf selection can yield an induction machine solution. However, there may be cases where the selection is not compact enough. In such cases a new permanent magnet motor design is required and a BLDC motor is a realistic choice from a cost perspective. It is found that for such applications, the most critical design factor is to avoid magnet demagnetisation. The thermal loading is not a design factor owing to the very small application times involved. However, a thermal check on the obtained design is always advisable