Motor Control: Lesson 9 - Motor Speed Control Flashcards
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. rotor
To operate a wound rotor motor at full speed, the rotor windings must be ______.
a. connected
b. open
c. shorted together
c. shorted together
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. Frequency control
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
c. slip rings
Single-phase motor speed control circuits use SCR or ______ to control power to the motor for speed control.
a. diacs
b. diodes
c. triacs
c. triacs
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
b. firing
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
b. 1440 RPM
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. converter
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
b. DC bus
The VFD’s AC output is a ______ waveform.
a. pulse width modulation
b. sine
c. square
a. pulse width modulation
The voltage source for the VFD is ______-phase AC.
a. single
b. 3
a. single
The output voltage to the motor is ______ -phase AC.
a. single
b. 3
b. 3
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. transformer
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. full wave bridge
______ NPN transistors are used in the inverter section.
a. Six
b. Three
a. Six
The inverter section converts the filtered ______ voltage to pulse width modulated ______ voltage.
a. AC / DC
b. DC / AC
b. DC / AC
The transistor switches in the inverter stage are driven by the ______.
a. control logic
b. DC bus
a. control logic
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
True
Drum brakes in an automobile are an example of ______ braking.
a. electrical
b. mechanical
b. mechanical
Dynamic, flux, injection, and regenerative are four types of ______ braking techniques.
a. electrical
b. mechanical
a. electrical
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
c. injection
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
b. Dynamic and regenerative
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. feedback
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. closed-loop
Another name for a sensorless vector drive is the ______ vector drive.
a. closed-loop
b. open-loop
b. open-loop
Vector drives are ______ expensive than other variable frequency drives.
a. less
b. more
b. more
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
True
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%
c. 10%
