When you reconnect the motor to a power source of
coil. When coils are placed in stator slots, they can be
220 volts ac, the run windings must be connected in
wound in place by hand or wound in a coil winder on
forms, and then placed in the slots of the stator.
series by placing the two connecting bars as shown in
figure 7-71, view B.
Capacitors used with single-phase motors for
starting should be checked by means of a capacity tester.
By tracing through the two series and parallel
This also applies to the capacitor-start, capacitor-run
bar-connected circuits, you will note that the starting
type of motors.
winding operates on 110 volts regardless of a parallel
or series connection.
MOTOR AND GENERATOR AIR
Figure 7-72 is a diagram of a four-pole, split-phase
COOLERS
motor. The type of winding used on both the running
Some large electric motors and generators, such as
and starting windings is the spiral winding. The
difference between the two windings is their impedance
propulsion generators and motors, are equipped with
surface-type air coolers. In this system the air is
and position in the stator slots. The running winding has
circulated by fans on the rotor in a continuous path
a low resistance and a high reactance (because of many
through the machine windings and over the
turns of large wire), and the starting winding has a high
water-cooled tubes of the cooler. The ceder is of
resistance and a small reactance (being wound of small
double-tube construction (one tube inside another).
or high-resistance wire).
This minimizes the possibility of damage due to water
The running winding is placed in the bottom of the
leakage. I&location of the air cooler on a generator is
slots, and the starting winding is placed on top of the
shown in figure 7-73.
running winding. Both windings are energized in
The air and water sides of air cooler tubes must be
parallel at starting. The currents are out of phase with
kept as clean as possible because foreign deposits will
each other, and the combined effects produce a rotating
decrease heat transfer. When you are required to clean
field that starts the motor (some motors use capacitors
the air side of the tubes, the individual tube bundles may
for starting). When the motor has almost reached
be removed and washed with hot water or cleaned with
normal speed, the centrifugal switch opens the starting
a steam jet. The water side of cooler tubes must be
winding circuit, and the motor operates as a single-phase
cleaned following instructions contained in the NSTM,
induction motor.
chapter 254.
A pole for the running or the starting winding in a
When a leak between an inner tube and the tube
single-phase motor is made up of more than one coil.
sheet occurs, water will seep from the cooler head
These coils differ from each other in size and, depending
through the leaky joint into a leak-off compartment and
on the winding specifications, in the number of turns per
out the leakage drain. If a leak in an inner tube, water
will seep into slots in the outer tube where it is carried
to a leak-off compartment and out the leakage drain.
The leakage drain line is equipped to give a visual
indication of the presence of water in the line.
Figure 7-73.--Generator equipped with an ailr cooler.
Figure 7-72.--A four-pole, split-phase motor.
7-48
