Flashcards in Quiz #6 Deck (19):
In a three-phase, squirrel-cage type, induction motor,
the primary rotating magnetic field is established by the
application of a three-phase
to the stator windings
In general, polyphase induction motors can be started
on full line voltage by means of __________.
The speed of a three-phase squirrel-cage induction-type
motor operating in a fixed frequency system is varied by
changing the __________.
number of stator poles
If there is a reduction in the normally supplied frequency
to a 120/240 volt, three-phase AC current motor from 60
hertz to 55 hertz, the motor would __________.
run at a slower speed
In a 15 HP induction-type motor with a cage rotor, the
current required at standstill to produce starting torque
is approximately __________.
five times the full load current
If a three-phase induction motor is operated under a
light load and it develops an open in one of its supply
lines, the motor will __________.
continue to run, but will vibrate and have reduced torque
If a three-phase induction motor malfunctions and drops
to a single-phase (one supply line open) __________.
the motor will continue to run if it is not heavily loaded
A characteristic of a wound-rotor induction motor, with a
high resistance rotor winding, is __________.
high starting torque
Regarding an induction motor, the power developed by
the rotor automatically adjusts itself to the __________.
power required to drive the load
The synchronous speed of an induction motor is the
speed of the rotating field
The direction of rotation of an induction motor is
the same as the direction of the rotating fields
One item listed on the name plate of a cargo pump
motor is 'degrees centigrade rise.' This number is based
an ambient temperature of 40° C
The rotor of a synchronous motor operates in
synchronism with the rotating field because
the rotor is magnetically locked into step with the rotating magnetic field by the excitation current
The most common source of excitation for the rotor of a synchronous motor is a/an __________.
The purpose of a cage rotor winding placed on the rotor
of a synchronous motor is to __________.
start the machine as an induction motor
The speed of a synchronous motor is varied by
changing the input frequency
Which of the listed motors will operate at the highest
RPM, assuming that each operates at the same
a four-pole synchronous motor under normal load
The variable resistance placed in the rotor circuit of a
wound-rotor induction motor provides for __________.