Theory- Motors
Mastering AC Induction Motors Quiz
Test your knowledge on the theory and operation of AC induction motors through our comprehensive quiz. With 45 carefully crafted questions, this quiz is an excellent resource for anyone looking to deepen their understanding of motor technology.
Topics covered include:
- Motor components
- Centrifugal switches
- Wound rotor motors
- Slip rings
What part of an AC induction motor rotates
The stator
The rotor
The start winding
The centrifugal switch
What is the "normal" state of a centrifugal switch change state
N.O
N.C
SPDT
None of the above
At about what rotor speed does the centrifugal switch change state?
100% rated speed
75% rated speed
50% rated speed
10% rated speed
If the start winding is damaged and open, what could be the motor symptom?
Overheating
Running backwards
Won`t start on it`s own
Low torque
You need to select a single phase motor for a cement mixer, which is your best choice?
Split phase
Capacitor start
Resistive start
Inductive start
When does an AC induction motor slip the most?
At no load
At full load
When running over FLA
When stalled (locked rotor)
Why does an AC motor draw more current when loaded?
Because the centrifugal switch is open
Because it slips more
Because the run winding is larger than the start winding
Because the power factor is worse
If an AC motor is overheating, what is a likely cause?
Wrong start winding installed
Wrong overloads installed
Wrong load attatched
Wrong current supplied
How many physical poles are found in a 4 pole, 3 phase motor
4
6
8
12
How many poles are found in a 4 pole, single phase motor?
4
6
8
12
If an AC motor`s name plate indicated 1160RPM, how many poles do you think it has?
2
4
6
12
How many mechanical degrees apart are the actual magnetic poles within a 2 pole, 3 phase motor located?
60
120
180
360
An AC motor is blowing fuses immediately. This is likely caused by:
Damage due to an open winding
A bad centrifugal switch
Damage due to a shorted winding
Too much load attatched
What measurement tool would you grab first if your motor was blowing fuses?
Clamp on ammeter
Megger
Voltmeter
Ohmmeter
How can you tell a 3 phase motor is single phasing?
It runs slowly
Does not start or is noisy
2 of the fuses are blown
Measures O.L. With a meter
You measure the resistance of the windings (line to line) on a 3 phase motor. The name plate indicates the voltage is 600V, the FLA is 10.6A, the HP is 10hp. The 3 windings measure 8.6 ohms each. What do you conclude?
The motor windings are likely ok
The motor winding insulation is likely damaged
The motor windings are likely shorted
The motor windings are likely open
You measure the resistance of the winding insulation on a 3 phase motor. Your digital multimeter indicates O.L. For all three phases to ground. What do you conclude?
The motor windings are likely ok
The motor winding insulation is likely damaged
The motor windings are likely shorted
The motor windings are likely open
How many slip rings will a round rotor motor have
2
3
4 for two pole, 6 for 4 pole
What is the purpose of the slip rings on a wound rotor motor
Brings 3 phase power to the rotor
Moves 3 phase power out of the rotor
Adds resistance to the stator circuit
Adds resistance to the rotor circuit
Why do wound rotor motors exist?
Allows ac motor speed control
More efficient and reliable then a conventional induction motor
Allows a 3 phase motor to run on single phase
Runs at sync. speed
How does a wound rotor motor work
High rotor resistance allows the rotor to slip while limiting current
Low resistance allows the rotor to slip while limiting current
Rotor resistance drops a portion of the stator voltage, limiting slip
None of the above
What is the range of speeds I can expect to get from a 4 pole wound rotor motor?
300-1750 RPM
900-1750 RPM
1800-3525 RPM
About zero to full load speed
If I suspect I am looking at a wound rotor motor, what additional clues could I look for?
A 3 phase alternator near by
A centrifugal switch
An external DC source for the rotor
An external resistor bank
If the rotor circuit is open, how will the wound rotor motor behave?
It will only run at full speed
It will blow fuses
It won`t turn
It will only run at 50% speed
If the rotor circuit is shorted, how will the wound motor behave?
It will only run at full speed
It will blow fuses
It won`t turn
It will only run at 50% speed
Adding resistance to the rotor circuit:
Speeds the motor up
Slows the motor down
Makes the rotor slip less
Reduces the sync speed
The stator of a wound rotor motor:
Is connected to the 3 phase voltage by slip rings
Is connected to the external resistance by slip rings
Is similar to a split phase motor stator
Is similar to a 3 phase induction motor`s stator
How many slip rings will a synchronous motor have?
2
3
4 for two pole, 6 for 4 pole
0
What is the purpose of the slip rings on a synchronous motor?
Brings DC power to the rotor
Adds resistance to the stator circuit
Adds resistance to the rotor circuit
Moves 3 phases out of the rotor
Why do synchronous motors exist?
Used for power factor corection
More efficient and reliable then a conventional induction motor
Always runs at sync.speed
A and C
Which winding is found on the rotor?
The 3 phase winding
The wound rotor winding
The stator winding
The salient winding
What type of voltage is the salient field poles connected to?
Single phase AC voltage
3 phase AC voltage
DC voltage
What type of voltage is the stator winding connected to?
Single phase AC voltage
3 phase AC voltage
DC voltage
In what order is a synchronous motor started?
First the salient field poles, then the stator winding?
First the stator windings, then the salient field poles
Stator winding and salient field poles at the same time
To make a synchronous motor run at a leading PF, I must:
Connect a capacitor in series
Reduce the salient field pole voltage
Increase the salient field pole voltage
Increase the amortisseur winding voltage
Will a synchronous motor run without an external DC source?
Yes, but it will slip
No, it won`t start
Yes, but the current will be high
No, it will trip the overloads
If the frequency is 50Hz, how fast will a 2 pole warren clock motor rotate?
3600RPM
3550RPM
3000RPM
2950RPM
How many turns of wire is in the shading ring
1 turn of heavy wire
1 turn of light wire
Many turns of heavy wire
Many turns of light wire
Why does the magnetic field avoid the area of the shading ring while the voltage is increasing during the first third of the alternation?
The shading ring produces a magnetic field that opposes it
The shading ring produces a magnetic field that supplements it
The shading ring produces no magnetic field
Which single phase motor produces the most noise?
Warren clock
Shaded pole
Universal
Split phase
Which motor runs at sync. speed?
Warren clock
Shaded pole
Universal
Split phase
Which motor produces the most torque?
Warren clock
Shaded pole
Universal
Split phase
Which motor would you find in a fan?
Warren clock
Shaded pole
Universal
Split phase
Which motor has a commutator?
Warren clock
Shaded pole
Universal
Split phase
Which motor would you find in an old school record player?
Warren clock
Shaded pole
Universal
Split phase
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