174

ELECTRICAL APPARATUS

These brushes, B^ are carried by the rotating squirrel-cage
secondary, Si, of a small auxiliary motor. The primary of this,
PI, is mounted on the power shaft, A, of the main motor, and
carries the commutator, Ci, which receives current from the
brushes, BI.

These brushes are speeded up to or near synchronism by some
means, as hand wheel, JJ, and gears, (?, and then allowed to slow
down. Assuming the brushes were rotating in counter-clock-
wise direction. Then, while they are slowing down, the (ex-
ternal) squirrel-cage rotor, Si, of the auxiliary motor starts and

FIG. 61.-

-Rotary terminal sngle-phase induction motor with controlling
motor.

speeds up, in clockwise direction, and while the brushes, BI,
come to rest, Si comes up to full speed, and thereby brings the
brushes, BG, of the power motor up to speed in clockwise rotation.
As soon as J30 has reached sufficient speed, the power motor gets
torque and its rotor, So, starts, in counter-clockwise rotation.
As S0 carries PI, with increasing speed of S0 and Pi, Si and with
it the brushes, jB0, slow down, until full speed of the power motor,
So, is reached, the brushes, BQ, stand still, and the brushes, JSi,
by their friction -on the commutator, Ci, revolve together with
Ci, PI and So.
In whichever direction the brushes, Bi9 are started, in the
same direction starts the main motor, So.