Rotary Converters.—The synchronous or rotary converter consists of a synchronous motor and a direct current generator combined in one machine. It resembles a direct current generator with an unusually large commutator and an auxiliary set of collector rings.
Ques. In general, how does a rotary converter operate?
Ans. On the collector ring side it operates as a synchronous motor, while on the commutator side, as a dynamo.
Its design in certain respects is a compromise between alternating current and direct current practice most noticeably with respect to the number of poles and speed.
Ques. Upon what does the speed depend?
Ans. Since the input side consists of a synchronous motor, the speed is governed by the frequency of the alternating current supplied, and the number of poles.
Fig. 2,035.—Diagram of two phase rotary converter. This is identical with the single phase machine with the exception that another pair of collector rings are added, and connected to points on the winding at right angles to the first, giving four brushes on the alternating side for the two phase current. The pressure will be the same for each phase as in the single phase rotary. Neglecting losses the current for each phase will be equal to the direct current × 1 ÷ / √2 = direct current × .707.
Fig. 2,034 is a diagram of a ring wound rotary converter. This style winding is shown to simplify the explanation. In practice drum wound armatures are used, the operation, however, is the same.