Hawkins Electrical Guide v. 06 (of 10)

Hawkins Electrical Guide v. 06 (of 10) - Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

The almost universal adoption of the alternating current system of distribution of electrical energy for light and power, and the many inherent advantages of the alternating current motor, have created the wide field of application now covered by this type of apparatus. As many central stations furnish only alternating current, it has become necessary for motor manufacturers to perfect types of alternating current motor suitable for all classes of industrial drive and which are adapted for use on the kinds of alternating circuit employed. This has naturally resulted in a multiplicity of types and a classification, to be comprehensive, must, as in the case of alternators, divide the motors into groups as regarded from several points of view. Accordingly, alternating current motors may be classified: Figs. 1,585 to 1,588.Synchronous motor principles: I. A single phase synchronous motor is not self-starting. The figures show an elementary alternator and an elementary synchronous motor, the construction of each being identical as shown. If the alternator be started, during the first half of a revolution, beginning at the initial position ABCD, fig. 1,585, current will flow in the direction indicated by the arrows, passing through the external circuit and armature of the motor, fig. 1,586, inducing magnetic poles in the latter as shown by the vertical arrows. These poles are attracted by unlike poles of the field magnets, which tend to turn the motor armature in a counter-clockwise direction. Now, before the torque thus set up has time to overcome the inertia of the motor armature and cause it to rotate, the alternator armature has completed the half revolution, and beginning the second half of the revolution, as in fig. 1,587, the current is reversed and consequently the induced magnetic poles in the motor armature are reversed also. This tends to rotate the armature in the reverse direction, as in fig. 1,588. These reversals of current occur with such frequency that the force does not act long enough in either direction to overcome the inertia of the armature; consequently it remains at rest, or to be exact, it vibrates. Hence, a single phase synchronous motor must be started by some external force and brought up to a speed that gives the same frequency as the alternator before it will operate. A single phase synchronous motor, then, is not self-starting, which is one of its disadvantages; the reason it will operate after being speeded up to synchronism with the alternator and then connected in the circuit is explained in figs. 1,589 to 1,592. ......Buy Now (To Read More)

Product details

Ebook Number: 49252
Author: Hawkins, N. (Nehemiah)
Release Date: Jun 21, 2015
Format: eBook
Language: English