For single phase or two phase machines it is 1 to .7; for three phase, 1 to .612, or six phase, 1 to .7 or 1 to .613 depending upon the kind of connection used for the transformer.
For example, a two phase rotary receiving alternating current at 426 volts will deliver direct current at 600 volts, while a three phase rotary receiving alternating current at 367 volts will deliver direct current at 600 volts.
Fig. 2,049.—Commutating pole of Westinghouse commutating pole rotary converter. The commutating poles are similar in general construction to the main poles. The coils are of bare copper strap wound on edge. Ventilating spaces are provided between the pole and coil and between turns. The copper winding is bare except for a few turns at each end. Insulating bolts retain the turns in their proper position.
Ques. What difficulty would be encountered if other ratios of conversion than those given above were required?
Ans. An armature with a single winding could not be used.
It would be necessary to use a machine with two distinct armature windings or else a motor generator set.
Ques. What change in voltage is necessary between a converter and the alternator which furnishes the current?
Ans. The voltage must be reduced to the proper value by a step down transformer.