Articoli correlati a Dynamos and Dynamo Design; Direct Current Motors Alternating...
Dynamos and Dynamo Design; Direct Current Motors Alternating Currents Alternators Alternating-Current Apparatus - Brossura
Sinossi
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. 1905 edition. Excerpt: ...method; it will be described more in detail in Electric Railways. 41. The field magnets of series motors are sometimes provided with such a large number of turns that the field becomes fully magnetized when the current flowing is only a fraction of the full-load current of the motor. This gives a field that does not change greatly in strength for a considerable range of load, and thus tends to make the speed vary less with changes in the load, and also keeps the motor from sparking at moderate loads, on account of the strong field obtained. Street-railway motors are generally overwound in this way. SERIES MOTOR ON CONSTANT-CURRENT CrRCTTIT 42. It has already been mentioned that series motors have been operated to a limited extent in the past on constant-current circuits. Fig. 15 shows a series motor connected in an arc-light circuit, the current in which is kept at a constant value by means of a regulator on the dynamo D. "Since the current flowing through the field F of the motor is constant, the strength of field will be constant and the torque will also be constant. If the armature were allowed to run free, it would race very badly, the racing being worse than in the case of a series motor on a constant-potential circuit, because in the latter case the current in the field and armature is reduced and the torque correspondingly cut down as the speed increases, whereas in this case the current is kept constant and the torque remains the same. It is thus seen that the speed of a seriesmotor operated in this way would vary widely with the load, and such a motor without some regulating device would be unsuitable for operating machinery. Motors are now seldom if ever operated on arc circuits. Series motors on arc circuits are always more or...
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