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JATC Year 3: Motor Control Final > Motor Control: Lesson 9 - Motor Speed Control > Flashcards

Motor Control: Lesson 9 - Motor Speed Control Flashcards

1
Q

Wound rotor motor speed control is accomplished by inserting resistors in series with the ______ winding of the motor.

a. rotor
b. run
c. stator

A

a. rotor

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2
Q

To operate a wound rotor motor at full speed, the rotor windings must be ______.

a. connected
b. open
c. shorted together

A

c. shorted together

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3
Q

Changes in occurrence of the input voltage to adjust the motor speed for the wound rotor motor uses what method of speed control?

a. Frequency control
b. Manual
c. Time-operated

A

a. Frequency control

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4
Q

Rotor windings in wound rotor motors are connected to ______ on the shaft of the motor. Brushes allow those windings to be connected to external resistors to control the speed of the motor.

a. commutator
b. exciter
c. slip rings

A

c. slip rings

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5
Q

Single-phase motor speed control circuits use SCR or ______ to control power to the motor for speed control.

a. diacs
b. diodes
c. triacs

A

c. triacs

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6
Q

In a single-phase motor speed control, the thyristor controls power in the circuit by changing the ______ angle of the AC sine wave that drives the motor.

a. displacement
b. firing
c. phase

A

b. firing

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7
Q

A variable frequency drive provides a 48 hertz AC voltage to a 3-phase AC motor that has four poles per phase. What would be the synchronous speed of the motor with this voltage applied?

a. 1280 RPM
b. 1440 RPM
c. 1800 RPM

A

b. 1440 RPM

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8
Q

In a VFD, the ______ section of the VFD converts the incoming AC voltage into rectified DC voltage.

a. converter
b. DC bus
c. inverter

A

a. converter

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9
Q

Which section of a VFD conditions the pulsating DC output voltage waveform from the previous section, filtering and smoothing the waveform, to produce a pure DC waveform?

a. Converter
b. DC bus
c. Inverter

A

b. DC bus

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10
Q

The VFD’s AC output is a ______ waveform.

a. pulse width modulation
b. sine
c. square

A

a. pulse width modulation

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11
Q

The voltage source for the VFD is ______-phase AC.

a. single
b. 3

A

a. single

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12
Q

The output voltage to the motor is ______ -phase AC.

a. single
b. 3

A

b. 3

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13
Q

A ______ is used to convert the input voltage to the voltage required by the inverter section of the VFD.

a. transformer
b. voltage regulator

A

a. transformer

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14
Q

The converter section of the VFD uses a ______ to convert the incoming AC voltage to a pulsating DC voltage.

a. full wave bridge
b. half wave bridge

A

a. full wave bridge

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15
Q

______ NPN transistors are used in the inverter section.

a. Six
b. Three

A

a. Six

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16
Q

The inverter section converts the filtered ______ voltage to pulse width modulated ______ voltage.

a. AC / DC
b. DC / AC

A

b. DC / AC

17
Q

The transistor switches in the inverter stage are driven by the ______.

a. control logic
b. DC bus

A

a. control logic

18
Q

Braking of motors is used to reduce the time it takes a rotating motor to stop rotating after power is removed from the terminals.

True or False

A

True

19
Q

Drum brakes in an automobile are an example of ______ braking.

a. electrical
b. mechanical

A

b. mechanical

20
Q

Dynamic, flux, injection, and regenerative are four types of ______ braking techniques.

a. electrical
b. mechanical

A

a. electrical

21
Q

In ______ braking, a DC current is applied to two of the three windings in a three-phase motor.

a. dynamic
b. flux
c. injection
d. regenerative

A

c. injection

22
Q

Which two braking methods are most commonly used with VFDs?

a. Dynamic and flux
b. Dynamic and regenerative
c. Flux and injection
d. Injection and regenerative

A

b. Dynamic and regenerative

23
Q

More precise motor speed control can be accomplished using a vector drive, which uses ______ to modify the PWM output of the VFD.

a. feedback
b. programmed logic
c. resistors

A

a. feedback

24
Q

A(n) ______ vector drive uses a shaft encoder on the motor shaft to give shaft rotation data back to the drive.

a. closed-loop
b. open-loop

A

a. closed-loop

25
Q

Another name for a sensorless vector drive is the ______ vector drive.

a. closed-loop
b. open-loop

A

b. open-loop

26
Q

Vector drives are ______ expensive than other variable frequency drives.

a. less
b. more

A

b. more

27
Q

When troubleshooting VFDs, one should narrow problems to a specific system and eliminate external problems such as power source and motor load.

True or False

A

True

28
Q

Phase current to a VFD controlled motor load should vary less than ______ in each phase.

a. 5%
b. 7%
c. 10%
d. 12%
e. 15%

A

c. 10%

JATC Year 3: Motor Control Final (11 decks)

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