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American Railway Signaling Principles and Practices Alternating Current Relays X
American Railway Signaling Principles and Practices Alternating Current Relays
Chapter 10
Copyright 1927
Approx 56 pages
The alternating current relay performs the same function as the direct current relay, i.e., both types are provided with certain contacts to open or close circuits as desired, depending on whether these circuits are to be opened or closed when the relay is de-energized or energized as the case may be; in the alternating current relay, however, its motor mechanism or device which actuates the contacts is especially designed to operate on alternating current, while in the direct current relay this device, of course, is designed to operate on direct current. The entire mechanism of the alternating current relay, including windings, cores, armature and contact, is enclosed in a substantial case with exterior binding posts and glass sides to permit inspection. All cores of alternating current relays are laminated, being formed of thin painted sheets of steel stampings to prevent loss of power due to heating by eddy currents that would be generated to an undue extent by the alternating magnetic flux, if the core were solid as in direct current relays. The armature vane or rotor is the chief movable part of the relay, inasmuch as it furnishes the mechanical power to operate the contacts. A winding of a relay is the coiled conductor, which receives its energy from the outside source to make the relay function. A winding may be one coil or two or more coils wired in series or multiple. Nearly all relays are operated on the induction principle and are used either for track or line work, depending upon the source of control energy. The alternating current relay is either a single or two-element relay, depending upon the number of external control circuits. The two-element relay is sometimes called double-element relay or polyphase relay. It always has two windings and can be converted into a single-element relay by means of resistors or reactors used in connection with one of the windings. One of the windings in a two-element relay is connected to a constant local power source and called the "local" element ; it is usually wound for 15, 55 or 110 volts. The other winding is connected either to the track or line control, and is called the "control" element ; the control element is usually referred to as the track or line element.
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