Fig. 2,426.—Westinghouse voltage regulating primary relay; view of mechanism with case removed. This relay is practically a voltmeter arranged for making and breaking contacts with fluctuations of voltage. As shown in the figure, it consists essentially of a solenoid and a balance beam carrying two movable contact points on one end and attached to the solenoid core at the other. The oscillation of the core causes the contact carrying end of the beam to move between two stationary contact points connected to the auxiliary or secondary relay circuit. The stationary contact points are fitted with adjusting screws for either increasing or decreasing the distance between them, to the amount of change in the voltage required for making or breaking contact; in other words, for varying the sensitiveness of the relay. Means for varying the normal voltage which it is desired to maintain are provided in the spring attached to the balance beam and controlled by the micrometer adjusting screw. Increasing the tension of the spring results in lowering the normal voltage position. The relay is wound for a normal voltage of 110 volts, and has a range of adjustment from 90 to 130 volts. The total energy required for its operation is about 50 watts at normal voltage. Voltage transformers having at least 50 watts capacity are, therefore, required. The parts are: A, solenoid; B, solenoid core; C, end of balance beam; D, pivots, bearings; E, movable contact arm; F, upper stationary contact point; G, lower stationary contact point; H, adjusting screw; K, adjusting spring; L, feeder binding posts; M, auxiliary circuit and secondary relay binding posts.
Fig. 2,427.—Westinghouse voltage regulating secondary relay; view showing relay removed from oil tank. The secondary relay is practically a motor starting switch of the double pole double throw type, electrically operated through the contacts of the primary relay. It is provided with contact points of one-half inch rod. The relay is suitably connected for starting, stopping and reversing the motor and for properly operating the motor brake. The parts are: A, solenoid; B, laminated field; C, movable contact arm; D, stationary contact arms; E, removable brass contact points; F, terminal block; G, terminals.
Ques. Why are two relays used?
Ans. For the reason that a primary relay, of sufficient accuracy and freedom from errors due to temperature and frequency variations, could not be made sufficiently powerful to carry the relatively large current required for operating the motor.
Ques. What names are given to the relays?
Ans. Primary and secondary.
Ques. What difficulties were encountered in the operation of relays?