Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1916 Excerpt: ...ideal shape of an alternating electromotive force or current curve. The exact form of an alternating electromotive force curve in any given alternating-current generator or alternator depends upon the design and construction of the machine, and the exact form of an alternating-current curve depends upon the conditions of the circuit to which the current is supplied. For the sake of simplicity the most elementary type of dynamo has been chosen to illustrate the preceding principles. Such a machine could develop at best but a very low electromotive force, it would have little output and the frequency would be very small. In the common types of alternators used in practice, therefore, where the electromotive forces range from 1,000 to 13,000 volts, the outputs from 30 to 5,000 kilowatts, and the frequencies from 25 to 140 cycles per second, the higher electromotive forces are attained by increasing the number of turns of wire in the revolving loop, by increasing its speed of rotation and by strengthening the magnetic field; the greater outputs are attained by increasing the number of pairs of poles and the number of loops, the latter of which are composed of larger wire and are connected in multiple with the collector rings; the higher frequencies are attained by raising the speed of the revolving loop or loops, and by increasing the number of pairs of poles. 209. What difference is there between single-phase, two-phase and three-phase alternators? The simple electric generator presented in Fig. 34 is capable of delivering but a single alternating current and is therefore called a single-phase alternator. By the addition of another loop 90 degrees around from the loop a and another set of collector rings electrically connected thereto, two alternating currents...
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