Fig. 2,422.—Westinghouse polyphase motor operated induction regulator showing operating mechanism. The primary shaft is turned by means of a bronze worm wheel engaging a forged steel worm, provided with a ball bearing end thrust. This worm gear is housed in a separate casting bolted to the cover. The casting is made separate in order to permit close adjustment between the worm wheel and the worm to aid in counteracting the tendency to vibration. Finished surfaces on the worm gear casting are provided for mounting the motor and the brake. On the automatic regulator, the worm shaft is connected to the motor through a spur gear and pinion, which constitutes a compact driving device having very little friction. Provision is made for either alternating current or direct current motor drive. When a motor driven regulator is operated by hand, the brake must be held in the release position, otherwise it will be impossible to operate the regulator. In the hand operated regulator the spur gear is replaced by a hand wheel and the regulator is driven directly from the worm shaft.
Polyphase regulators have but little tendency to vibrate because the field across the air gap is the resultant of two or more single phase fields and is of a constant value at all times. This field rotates at a rate depending upon the number of poles and the frequency of the circuit. This produces a mechanical pull of constant value which rotates with the magnetic field varying its position from instant to instant.
It is evident that this pull is of an entirely different character from that produced by the single phase field and that there is no tendency to set up the vibration that the mechanical pull of the single phase regulator tends to establish.
Fig. 2,423.—General Electric adjustable compensation shunt. It is used as the compensating shunt for direct current voltage regulators. In operation, the shunt may be adjusted so as to compensate for any desired line drop up to 15 per cent. It is preferably placed in the principal lighting feeder but may be connected to the bus bars so that it will take the total current. The latter method is sometimes undesirable, as large fluctuating power loads on separate feeders might disturb the regulation of the lighting feeders. Adjustment is made by sliding the movable contact shown at the center of the shunt. This contact may be clamped at any desired point and it determines the pressure across the compensating winding of the regulator's control magnet. Where pressure wires are run back to the central station from the center of distribution, they may be connected directly to the pressure winding of the main control magnet, and it is unnecessary to use the compensating shunt.
There is, however, considerable torque developed, and the device for revolving the moving element must be liberally designed so as to withstand the excess torque caused by temporary overloads or short circuits.
Ques. In what respects do polyphase induction regulators differ in principle from single phase regulators?
Ans. The induced voltage in the secondary has a constant value, and the regulation is effected by varying the phase relation between the line voltage and the regulator voltage.
Ques. How is the primary wound?
Ans. It is wound with as many separate windings as there are phases in the circuit, and these primary or shunt windings are connected to the corresponding phases of the feeder.