Electrical variable-speed drives

The paper outlines the principles upon which the efficient control of speed of electrical machines is based, and classifies all the main types of variable-speed drive in accordance with these principles. The development of successful forms of drive is charted from the early machines using electromagnetic control to their modern equivalents using electronic control. The modern drives are described in some detail, and their main features tabulated to show the factors which should be taken into account when selecting a drive system.