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Page 92

| Figure 6-3 An induction regulator. |

| connected across (or in shunt with) the circuit to be regulated. The secondary or low-voltage winding is connected in series with the circuit. The primary (high-voltage) winding is mounted so that it can rotate on the axis of the secondary winding. The voltage induced in the secondary or series winding depends on the position of the primary winding. The high-voltage winding thus can be placed so that the voltage induced in the series winding will add or subtract from the input line voltage. When the load current is small, the primary will be rotated in one direction, thus lowering or bucking the line voltage. When the load current is larger, the primary will be rotated in the opposite direction, thus boosting it. The reactance of the secondary can cause a large voltage drop during the rotation of the primary. To avoid this drop (or cancel it out), a third coil is added and mounted on the movable core at a right angle to the primary winding and short-circuited on itself. The turning of the primary coil is usually controlled by means of a voltage-sensitive relay (called a contact-making voltmeter) connected in the output side of the circuit. |

| A second type voltage regulator, (Fig. 6-4) often called a Step-Type Voltage Regulator or a Tap Changing Under Load (TCUL) transformer, is more often found in electrical substations and is associated with the supply of large amounts of power. The connection of this type regulator in the circuit is the same as that of the induction-voltage regulator. The changes in voltage are accomplished by varying the ratio of transformation by changing the number of turns in the primary by means of taps connected as shown schematically in Fig. 6-5. Other arrangements accomplishing the same purpose include a separate winding (with the taps) which is capable of being reversed in connection so that the voltage within that separate winding can be added to or subtracted from that in the remainder of the primary winding. |

| The application of another small autotransformer capable of being connected across the taps makes the operation of tap changing under load successful. The function of this autotransformer is to aid in preventing the transformer from being disconnected from the line while stepping from tap to tap on the transformer winding. Figure 6-6 (on page 94) is a schematic diagram of how the tap-changing equipment operates under load. The selector |

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