Chapter Seven

Variable Frequency Operation of Induction Motors

1. Introduction

We saw in Chapter 6 the many attributes of the induction motor which have made it the preferred workhorse of industry. These include simple low-cost construction which lends itself to totally enclosed designs suitable for dirty or even hazardous environments; limited routine maintenance with no brushes; only three power connections; and good full-load efficiency. We have also seen that when operated from the utility supply there are a number of undesirable characteristics, the most notable being that there is only one speed of operation (or more precisely a narrow load-dependent speed range). In addition, starting equipment is often required to avoid excessive currents ...

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