Fig. 799.—Diagram showing connections of balancing set in three wire one dynamo system. The set consists of a motor and dynamo connected, and its operation is practically the same as a dynamotor.
Ques. How is the dynamotor used as an equalizer in the three wire system?
Ans. When thus used, the machine is connected as in [fig. 798]. When both sides of the system are balanced, there will be no current in the neutral lead N, and a small current will pass through the two armature windings of the dynamotor in series, both armatures acting as motors. If the load on one side of the system become larger than the load on the other side, there will be a greater drop in the leads connected to the overloaded side and consequently a lower voltage will exist over the larger load than exists over the smaller load. The armature winding of the dynamotor connected to the higher voltage will act as a dynamo, whose pressure will tend to raise the voltage of the more heavily loaded side.
The direction of the currents in an unbalanced three wire system that is being supplied with energy from a main dynamo is shown in the figure. The commutator at G is connected to the dynamo winding of the dynamotor and is supplying current to the upper or larger load, and the lower commutator is connected to the motor winding of the dynamotor and is taking current from the lightly loaded side.
Motor-Dynamo or Balancing Set.—A balancing set or balancer consists of a motor mechanically connected to a dynamo used to balance a three wire system. The operation of such a combination is practically the same as the dynamotor just described. The balancer is connected as shown in [fig. 799].
Fig. 800.—Holzer-Cabot type M motor-dynamo set. This combination is known as a booster, and is used to raise or lower the voltage on feeders. The motor is series wound and connected in series with one leg of the feeder. Thus, the voltage which the booster will add to the line will be directly in proportion to the current flowing in the feeder. The regulation is therefore automatic.