Ques. Upon what does the local armature current depend?
Ans. Upon the number of turns of the short circuited coils, their resistance, and the frequency.
Ques. How can the local currents be reduced to avoid heavy sparking?
Ans. 1. By reducing the number of turns of the short circuited coils, that is, providing a greater number of commutator bars; 2, reducing the frequency; and 3, increasing the resistance of the short circuited coil circuit: a, by means of high resistance connectors; or b, by using brushes of higher resistance.
Figs. 1,880 to 1,884.—Assembly and disassembled view of short circuiting device as used on Bell single phase repulsion induction motor. The armature, which is wound in a similar manner to those used in direct current motors, has a commutator, and brushes, which being short circuited on themselves, allow great starting torque, with small starting current. The motor starts by the repulsion principle, and on reaching nearly full speed, a centrifugal governor pushes the copper ring against the commutator segments, thereby short circuiting them, and the motor then operates on the induction principle.
Ques. What are high resistance connectors?
Ans. The connectors between the armature winding and the commutator bars, as shown in fig. 1,885.