These conditions require 720 inductors in series in the armature circuit, and as the armature is divided into six slots corresponding to the six poles, there will be 120 inductors per slot, and the coil surrounding each of the six teeth on the surface of the armature will consist of 60 turns. The connections must be such as to give alternate clockwise and counter-clockwise winding proceeding around the armature.
Fig. 1,527.—Diagram of six pole single phase revolving armature alternator, with monotooth or concentrated whole coil winding. For 3,000 volts at 900 revolutions per minute, 120 inductors are required. And in the case of a concentrated or monotooth winding they may be arranged in "whole coils" as above or in "half coils" (hemitropic) as in fig. 1,528.
Ques. In what other way could the inductors be arranged in concentrated coils?
Ans. They could be grouped in three coils of 120 turns each, as shown in fig. 1,528.
When thus grouped the arrangement is called a hemitropic winding, as previously explained.
Fig. 1,528.—Diagram of six pole single phase alternator with concentrated half coil or hemitropic winding of same capacity as in fig. 1,527. There are an equal number of inductors, but in this case arranged in three instead of six coils. In this winding the direction of winding is alternately reversed so that the induced pressures do not oppose one another.
Ques. What is the advantage, if any, of a half coil winding?