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 TM 5-683/NAVFAC MO-116/AFJMAN 32-1083
GREASE FITTINGS
AND
GREASE RELIEF PLUGS
OOLI N
EAL
CONDUIT BOX
Figure 41. Cutaway view of squirrel-cage induction motor.
torque limitations. It may be used for power factor
erations on an AC motor will encompass mainte-
improvement since a synchronous motor operates at
nance on the following components.
unity or a leading power factor (in addition to lag-
(1) Stator and rotor windings. The primary
ging power factor). They are also more efficient than
parts of a typical motor are (fig 44): the frame and
some induction or DC motors having the same
base that support the assembled motor; the stator
speed and power rating. But the higher cost, larger
which is the stationary part consisting of an iron
size per horsepower and lower starting torque are
core and insulated windings; and the rotor which is
the disadvantages that limit synchronous unit ap-
the rotating element. The term armature is often
plication.
used in lieu of rotor, particularly with DC motors
d. High-efficiency unit. This motor is specially de-
and for AC motors with commutators or collector
signed to reduce electrical losses as much as 50
rings and brushes. Most stator and rotor problems
percent so that less electricity is used over the en-
can be traced to winding failures. The life of a wind-
tire life of the motor. These motors also operate at
ing depends upon keeping it as near to its original
higher power factor values which help avoid power
factor penalties and reduce the cost of power factor
condition as long as possible. Insulation failure
correction. They can deliver longer service, are more
causes immediate outage time. The following points
reliable, and are more easily maintained than nor-
should be carefully examined and corrective action
mal efficiency motors.
taken during scheduled inspections to prevent op-
e. Components of AC machines. Maintenance op-
eration failures.
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