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Page 242

| Figure 13-5 Electromechanical relays: (A) Solenoid type-instantaneous, a-c or d-c; (B) balanced-beam type--instantaneous, a-c or d-c; (C) polar type--instantaneous, d-c (a-c used with rectifier); (D) armature or clapper type--instantaneous, a-c or d-c. (Courtesy, Westinghouse Electric Co.) |

| completes the tripping circuit that operates one or more circuit breakers. Since the disc is balanced against the pull of a spring, it is necessary to have a certain quantity of current flowing before the disc will begin to rotate. Once it has started, the speed of rotation will be proportional to the current flowing in the relay coil until the latter reaches an exceedingly high value. This relationship gives the relay an inverse-time characteristic; that is, the greater the current flowing in the coil, the sooner the relay contacts will close. In order to prevent the instantaneous closing of the relay contacts under heavy short circuits, a small torque compensator, or reactor, is placed in the circuit of the relay coil (Fig. 13-6B). This compensator acts upon the relay in such a way that a definite minimum time must elapse before the contacts will close, |

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