Quiz #6 Flashcards Preview

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Flashcards in Quiz #6 Deck (19):
1

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

2

In general, polyphase induction motors can be started
on full line voltage by means of __________.

across-the-line
starters

3

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

4

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

5

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

6

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

7

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

8

A characteristic of a wound-rotor induction motor, with a
high resistance rotor winding, is __________.

high starting torque

9

Regarding an induction motor, the power developed by
the rotor automatically adjusts itself to the __________.

power required to drive the load

10

The synchronous speed of an induction motor is the
__________.

speed of the rotating field

11

The direction of rotation of an induction motor is
__________.

the same as the direction of the rotating fields

12

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

13

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

14

The most common source of excitation for the rotor of a synchronous motor is a/an __________.

DC supply

15

The purpose of a cage rotor winding placed on the rotor
of a synchronous motor is to __________.

start the machine as an induction motor

16

The speed of a synchronous motor is varied by
__________.

changing the input frequency

17

Which of the listed motors will operate at the highest
RPM, assuming that each operates at the same
frequency?

a four-pole synchronous motor under normal load

18

The variable resistance placed in the rotor circuit of a
wound-rotor induction motor provides for __________.

speed control

19

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

1746 RPM