In construction, the transformers may be made exactly alike so that either may be used as main or teaser.
In order that the connections may be properly and conveniently made, the primary windings should be provided with 50% and 86.6% taps.
Fig. 2,177.—Three phase to two phase transformation with three star connected transformers. Two of the secondary windings are tapped at points corresponding to 57.7% of full voltage; these two windings are connected in series to form one secondary phase of voltage equal to that obtained by the other full secondary winding.
Ques. Describe another way of transforming from three to two phases.
Ans. The transformation may be made by three star connected transformers, proportioning the windings as in fig. 2,177, from which it will be seen that two of the secondary windings are tapped at points corresponding to 57.7 per cent. of full voltage.
Three Phase to Six Phase.—This transformation is usually made for use with rotary converters and may be accomplished in several ways. As these methods have been illustrated in the chapter on Converters (page 1,462), it is unnecessary to again discuss them here. Fig. 2,178, below shows the diametrical connection for transforming three phase to six phase.
Fig. 2,178.—Diagram of diametrical connection, three phase to six phase. It is obtained by bringing both ends of each secondary winding to opposite points on the rotary converter winding, utilizing the converter winding to give the six phases. This transformation of phases may also be obtained with transformers having two secondary windings.