Electrical Engineering ⇒ Topic : Induction regulator

INDUCTION REGULATORS

The induction regulator is really a special type of potential transformer with primary winding mounted on a cylindrical core that may be turned on its axis. The secondary winding is stationary. Both windings are mounted in slots, much as are the windings of an induction motor. A small air gap separates the stator from the rotor.

Regulators of this type are used to regulate the voltage on single-phase feeder circuits.Voltage drop in the feeder is compensated for by the voltage induced in the secondary of, the regulator.

A wiring diagram of the electrical connections is given in Fig.(a)

                                       Fig.(a). Wiring diagram of induction regulator in a transmission line

Since the maximum voltage induced in the secondary can be made to add directily or subtract directly from the line voltage by rotating the primary through an angle of 180°, the regulator is capable of 'boosting' or 'bucking' the line voltage; in the 900 position, no voltage is induced in the secondary. Fig (b), shows the electrical connections to the regulator feeder

                                                           Fig.(b). Circuit connections for reeder regulator

The induction regulator is essentially a specially constructed transformer in which the amount of flux set up by the primary is constant but that portion of the flux linking the secondary is variable. It thus has a variable co-efficient of coupling, somewhat similar to that in the constant-current transformer. In the induction regulator,however, the spacing between the axis of the coils is varied Fig.( c). The primary is wound On a movable, core while the secondary is fixed on the stator. In Fig.(c), the axes of both the coils conicide, and since maximum flux linkage is obtained, the secondary induced voltage is likewise a maxiinum. The primary may be rotated through 180°, thereby giving another maximum secondary voltage Fig. (c). The induction regulator position 1800 electrical degrees out of phase maximum-voltage position.with the first one.

                                                   Fig. (c). The induction regulator maximum-voltage position.

When axes of the coils are 90° apart, little or no voltage is induced in the secondary, since the flux linkage is at a maximum. However, the secondary coil may still carry considerable current due to the load circuit. With the little flux linking the coils, the secondary alone now sets up its own flux, and thus acts as a high-reactance coa in series with the load. In order to overcome this reactive volt drop, a short-circuited winding is placed on the rotor. The axis of the third winding is 90° from that of the primary winding Fig.(d)The secondary coil flux thus induces a voltage in the short-circuited winding, and the resultant current produces a flux opposing that caused by load current. This reduces the net flux, and hence the series reactive volt drop.

                                                             Fig.(d). Induction regulator with short circuited winding