WorksheetsQuiz Synchronous Motor 2025
Total questions: 23
Worksheet time: 12mins
For a synchronous motor Nm_??_Ns
lower than
higher than
equal with
What is the key characteristic of a synchronous motor?
It operates at variable speeds.
It operates at constant speed regardless of the load.
It operates only at high speeds.
It operates only at low speeds.
How is the constant speed of a synchronous motor achieved?
By using a single-phase AC supply.
By interaction between a constant and a rotating magnetic field.
By varying the load on the motor.
By using a variable frequency drive.
What type of magnetic field does the rotor of a synchronous motor produce?
A rotating magnetic field.
A constant magnetic field.
A pulsating magnetic field.
No magnetic field.
What type of current is used to excite the stator of a synchronous motor
DC
Single Phase AC
3-Phase AC
Pulsating DC
What is the synchronous speed of a motor determined by?
The load on the motor
The frequency of the AC supply.
The voltage of the AC supply.
The type of rotor used.
How is the rotor of a synchronous motor typically excited?
By a three-phase AC supply
By a single-phase AC supply.
By a DC supply or permanent magnets.
By an external mechanical force.
Why are synchronous motors not self-starting?
They require a high starting torque.
The rotor cannot initially synchronize with the rotating magnetic field.
They operate only at low speeds.
They require a single-phase supply to start.
What happens when the rotor reaches synchronous speed?
The rotor locks with the rotating magnetic field.
The rotor stops rotating.
The rotor speed exceeds the synchronous speed.
The rotor operates as an induction motor.
What happens if the load on a synchronous motor exceeds its capacity?
The motor continues to operate at synchronous speed
The motor slows down but does not stop.
The motor falls out of synchronization and stops.
The motor increases its speed to handle the load.
How does a synchronous motor improve the efficiency of a system?
By operating at variable speeds.
By reducing the load on the alternator.
By maintaining a constant speed and improving power factor.
By reducing the supply voltage.
For an Induction and Synchronous Motor, armature winding is located on..
Rotor
Stator
What is the graph between armature current and field current in a synchronous motor called?
Torque-speed curve
Efficiency curve
V-curve
Power factor curve
A 4-pole synchronous motor is connected to a 50 Hz supply. What is its speed in rpm?
157.1
1000
1500
1800
A 6-pole synchronous motor is connected to a 50 Hz supply. What is its speed in rad/s?
10.47
1000
1500
104.7
To achieve a synchronous speed of 1200 rpm with a 60 Hz supply, how many poles must the machine have?
2
4
6
8
If the mechanical speed of a synchronous motor is 157.08 rad/s at 50 Hz, what is the number of poles?
4
12
24
38
A 3-phase Y-connected synchronous motor has a terminal voltage of 480 V. What is the phase voltage?
160 V
480 V
277.1 V
240V
For a Y-connected machine, if the phase current is 50 A, what is the line current ?
28.9 A
50 A
16.6 A
35.4 A
A 200 kVA, 480 V, Y-connected generator is operating at rated conditions. What is its rated line current?
240.6 A
0.24 A
138 A
416 A
200 kVA, 480 V, Delta-connected generator is operating at rated conditions. What is its rated line current?
240.6 A
0.24 A
138 A
416 A
Slips for synchronous machine usually at 2% to 8%
TRUE
FALSE
With 1-2 words, describe your feeling
