The Three-Wire Generator

Author: E.E. Kimberly

The use of the balancer set to provide voltage balance on a three-wire system is open to the objection that the balancer requires service and attendance and requires power for its operation in addition to a considerable capital investment. These objections have been almost entirely overcome by the use of a balancer coil due to Dobrowolsky. As shown in Fig. 29-6, the balancer coil is simply a pair of reactor coils connecting points 180 electrical degrees apart on the armature winding and being themselves connected. The point at the reactor-coil connection is connected to the middle line of the three-wire system.

Fig. 29-6. Three-Wire System by Dobrowolsky Coils

Inasmuch as any pair of reactor coils connects two points on the armature 180 electrical degrees apart, the voltage across a pair of coils is alternating and the alternating current in the coils is small and similar to the exciting current of a transformer. However, the direct current of load unbalance flows freely in the coils. The coils are wound on separate iron cores mounted on the armature, or are wound on separate cores outside the machine. With coils mounted on the armature, only one slip-ring is necessary; whereas, with separate cores outside the machine, two or more slip-rings are necessary.