INTRODUCTION
The selection process often highlights difficulties in three areas. Firstly, as we have discovered in the preceding chapters, there is a good deal of overlap between the major types of motor and drive. This makes it impossible to lay down a set of hard and fast rules to guide the user straight to the best solution for a particular application. Secondly, users tend to underestimate the importance of starting with a comprehensive specification of what they really want, and they seldom realise how much weight attaches to such things as the steady-state torque–speed curve, the inertia of the load, the pattern of operation (continuous or intermittent) and the question of whether or not the drive needs to be capable of regeneration. And thirdly, they may be unaware of the existence of standards and legislation, and hence can be baffled by questions from any potential supplier.
The aim in this chapter is to assist the user by giving these matters an airing. We begin by drawing together broad guidelines relating to power and speed ranges for the various types of motor, then move on to the questions which need to be asked about the load and pattern of operation, and finally look briefly at the matter of standards. The whole business of selection is so broad that it really warrants a book to itself, but the cursory treatment here should at least help the user to specify the drive rating and arrive at a shortlist of possibilities.