February 2013
Beginner to intermediate
440 pages
14h 25m
English
Content preview from Electric Motors and Drives, 4th Edition
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Chapter Four
D.C. Motor Drives
1. Introduction
Until the 1960s, the only satisfactory way of obtaining the variable-voltage d.c. supply needed for speed control of an industrial d.c. motor was to generate it with a d.c. generator. The generator was driven at fixed speed by an induction motor, and the field of the generator was varied in order to vary the generated voltage. For a brief period in the 1950s these ‘Ward Leonard’ sets were superseded by grid-controlled mercury arc rectifiers, but these were soon replaced by thyristor converters which offered cheaper first cost, higher efficiency (typically over 95%), smaller size, reduced maintenance and faster response to changes in set speed. The disadvantages of rectified supplies are that the waveforms ...
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