alternating currents displaced in phase from one another, and he thus made possible by means of the induction motor, the use of polyphase currents for power purposes.
Ques. What is the difficulty encountered in starting a motor with single phase current?
Ans. A single phase current requires either a synchronous motor to develop mechanical power from it, or a specially constructed motor of dual type, the idea of which is to provide a method of getting rotation by foreign means and then to throw in the single phase current for power.
Fig. 1,376.—Diagram of six phase winding with star grouping, being equivalent to a three phase winding in which the three phases are disconnected from each other and their middle points united at a common junction.
Fig. 1,377.—Diagram of six phase winding with mesh grouping.
Six Phase and Twelve Phase Windings.—These are required for the operation of rotary converters. The phase difference in a six phase winding is 60 degrees and in a twelve phase winding 30 degrees. A six phase winding can be made out of a three phase winding by disconnecting the three phases from each other, uniting their middle points at a common junction, as shown by diagram fig. 1,376. This will give a star grouping with six terminals.
In the case of a mesh grouping, each of the three phases must be cut into two parts and then reconnected as shown in fig. 1,377.
