Essentials of electrical engineering; a text book for colleges and technical schools

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. 1915 Excerpt: ...produced in the iron core by coil P, f = the frequency of the alternating-current supply circuit, Np = the number of series turns in coil P, N. = the number of series turns in coil S, See Chapter 2, Section 13. The flux in the iron must decrease from its maximum 0„ to zero in one-fourth of a cycle. The average rate of flux change is, therefore, Y = 4-/, (1) 4? and the average electromotive force induced in coil P is the product of the average rate of change in the flux and the number of series turns in the coil. Ea. = 4fc»/#P Io"8. (2) Since the ratio of the effective electromotive force to the average electromotive force is i.n, Ep = 4.440„/iVp io8. (3) Assuming that the flux set up by coil P is confined to the iron core, the electromotive force induced in coil 5 is E. = 4.44»/tf. io"8-(4) If the terminals of coil S are connected through a resistance as shown in the figure, current flows in the windings of the coil. The current in coil 5 tends to establish in the iron core a flux opposed to that set up by coil P and the counter-electromotive force induced in coil P is reduced. The equilibrium of the system is thus destroyed, and the current in coil P increases until it neutralizes the magnetic effect of coil S. As the current in coil P increases, the resistance drop is no longer negligible and equilibrium is reestablished with a counterelectromotive force less than the applied electromotive force. Equilibrium in a transformer is, then, maintained by an automatic change in the current flowing in the primary coil. The conditions are analogous to those in a shunt motor, the speed of which decreases as the load increases, so that the torque developed in the motor armature is automatically adjusted to equal the counter torque due...