Ans. It is necessary to have, as a minimum, two coils per phase per pole in three phase work.
Ques. What is the effect of only one coil per phase per pole?
Ans. The wave form will be distorted as shown in fig. 1,247.
Ques. What is the least number of coils per phase per pole that should be used for two and three phase alternators?
Ans. For three phase, two coils, and for two phase, three coils, per phase per pole.
Single or Monophase Current.—This kind of alternating current is generated by an alternator having a single winding on its armature. Two wires, a lead and return, are used as in direct current.
An elementary diagram showing the working principles is illustrated in fig. 1,249, a similar hydraulic cycle being shown in figs. 1,250 to 1,252.
Fig. 1,249.—Elementary one loop alternator and sine curve illustrating single phase alternating current. There are three points during the revolution at which there is no current: at 0° the position shown, 180°, and 360°; in other words, at the beginning, middle point and end of the cycle. The current reaches a maximum at 90°, reverses at 180°, and reaches a maximum in the reverse direction at 270°.