Induction Regulators

Induction Regulator

An induction voltage regulator enables a smooth variation of the output voltage, whereas in a tap-changer transformer, the output voltage can be controlled only in discrete steps. In induction voltage regulator, the output voltage is controlled by varying the angle between the magnetic axes of primary and secondary windings. In tap-changer, the output voltage is regulated by altering the turns ratio.

An induction voltage regulator may be single-phase or three-phase and in both the types, the rotor moves only through a limited angle, usually 0° to 180° (equal to one pole pitch).

Single-phase Induction Regulator

Single-phase Induction Regulator It consists of a stator and a rotor and for convenience in operation, the rotor shaft is vertical. Since the rotor does not rotate continuously, induction voltage regulators in larger sizes, may be immersed in oil for cooling purposes. A handwheel, through rack and pinion arrangement, controls the rotor movement and, therefore, the output voltage. For automatic voltage regulation, the rotor movement is carried out by a small driving motor and a voltage relay sensitive to the output voltage variations. If the output voltage deviates from the desired value, the relay operates the driving motor in one direction or the other and stops it when the desired voltage is attained.

The primary winding is placed in the rotor slots, since it has to carry smaller current and has smaller conductor area. No slip rings are required to feed the primary winding, since the rotor movement is restricted from 0° to 180°. Flexible leads are suficient to feed the power to primary winding. The secondary winding, connected in series with the outgoing lines, is housed in the stator slots, due to larger conductor area. In addition to the primary winding,the rotor also carries a short circuited compensating winding whose magnetic axis is always 90°away from that of the primary winding.

Three-Phase induction Regulator

A three-phase induction voltage regulator resembles closely a three-phase slip-ring induction motor. The rotor carries the primary winding and the stator has the secondary winding as in the case of single-phase type. Three-phase primary winding is connected in star whereas the 3-phase secondary is connected in series with the load as large sizes, the induction regulator is oil-immersed in a tank like an ordinary transformer Rotor movement is carried out in the same manner as in a single-phase induction regulator.

When the induction voltage regulator is connected to 3-phase supply, three-phase currents in the three phase primary winding produce a constant amplitude rotating magnetie field as in a 3-phase induction motor. This rotating magnetic field induces e.m.fs, in the secondary winding whose magnitudes depend only on the ratio of primary to secondary turns and are independent of the rotor position. When the rotor position is changed with respect to stator, the magnitude of secondary e.m.fs. remains constant but their phase is altered with respect to primary voltages.