Quiz #6 Flashcards Preview

Applied Electricity > Quiz #6 > Flashcards

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
voltage supply
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
on __________.

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 __________.

DC supply


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 __________.

speed control


What is the rotor speed of a four pole, 60 cycle, induction motor operating at full load with 3% slip?

1746 RPM