A three-phase induction motor is an electric motor that runs on a three-phase AC supply. It's also known as a synchronous motor because it operates at a different speed from synchronous momentum.  Three-phase induction motors are known for being robust, efficient, and able to run under variable load conditions. They are built for everyday use in any environment.  Here's how a three-phase induction motor works: A current is applied through the stator, which induces a magnetic field. The magnetic field causes the rotor current to be induced, instead of electrical connections. The... Show more

A three-phase induction motor is an electric motor that runs on a three-phase AC supply. It's also known as a synchronous motor because it operates at a different speed from synchronous momentum. 

Three-phase induction motors are known for being robust, efficient, and able to run under variable load conditions. They are built for everyday use in any environment. 

Here's how a three-phase induction motor works:
A current is applied through the stator, which induces a magnetic field.
The magnetic field causes the rotor current to be induced, instead of electrical connections.
The rotational speed of the shaft and the applied torque depends on the operating frequency and the number of pole pairs in the motor's windings.
The unidirectional rotating magnetic field developed in air gap causes the motor to self-start. 

Three-phase induction motors consist of two parts:
Stator: A three-phase static winding
Rotor: A rotor winding which is a short-circuited winding 

Some types of three-phase motors include:
Plain or squirrel cage induction motors
Double squirrel cage motors
Slip-ring or wound-rotor induction motors 

Related:

Wireman Practice Test: Synchronous Motor

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Wireman Practice Test: Three Phase Induction Motor

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25 Questions

1. Which one of the following is not a reason for humming and chattering in a DOL starter?

Welded auxiliary contactImproper voltage for NVCOpen shading bandDust or Rust on pole faces

2. A three phase 1.2 KW, 440V, 50 cycles motor, starter use is...............

DOL starterOil immersed starterAuto transformer starterStar/ Delta starter

3. Which one is the cause to move the rotor in three phase induction motor?

Rotating Magnetic Field onlyThe emf induced in the rotor barsThe interact in between the stator and rotor magnetic field.The rotor magnetic field only

4. A 3 phase slip ring induction motor has ....................

Double cage rotorWound rotorAll of theseShort circuited rotor

5. In the star-delta starter method the voltage applied across the stator winding is ....

1/ (3)1/2 times the supply voltageEqual to the supply voltageNone of these1.732 times the supply voltage

6. What is the name of the part marked as X given below?

BrushesBearingsShaftSlip rings

7. What type of bolt is used while erecting slide rails for fixing motors?

Anchor BoltWing nutBed boltCoach screw

8. What is the name of the starter symbol given below?

D.O.L starterAutomatic star/delta starterAuto transformer starterSemi automatic star/delta starter

9. In the manual star delta starter, the stop button connection is in series with the.....

No-volt coil and start buttonOver load relay contactsNo-volt coil and load relay contactNo-volt coil

10. The stator ending of a three phase slip ring induction motor has 4 poles. How many numbers of poles are there in rotor winding

8462

11. Inching operation is also called as..............

StoppingStartingBreakingJogging

12. Stator of an induction motor contains three phase winding placed at .........

180 Electrical degree120 Electrical degree90 Electrical degree60 Electrical degree

13. What is the name of the starter symbol given below?

Star delta starterRheostatic starterDirect on-line starterAutotransformer starter

14. In a three phase induction motor started by a DOL starter the short circuit current is protected by.............

Protective earth conductorBack-up FusesNo-volt coilOver load relay

15. The star delta starter used in ...................

PumpsFlour millsAll of theseMachine tool drive

16. Which of the following current level of motor is to set in the over load relay?

Full load currentActual load currentMore than the full load currentLess than the actual load current

17. The frequency of the induced emf in an induction motor is ..............

Same as the supply frequencyLesser than the supply frequencyNoneGreater than the supply frequency

18. The three phase squirrel cage motors can be classified according to their electric characteristics. Which of the following classification motor is used for 3 phase compressor motor?

Class BClass AClass CClass D

19. When load increases the power factor of an induction motor becomes.......

ConstantLeadingMore and more laggingUnity

20. The shaft of an induction motor is made from..........

High speed steelCast ironStainless steelCarbon Steel

21. The nominal trip range of the bimetallic relay is.................. percentage of the nominal trip rating of the heating unit.

85 to 115120 to 13555 to 8065 to 75

22. DOL starters are used to start the AC motor only up to..............

1 HP4 HP3 HP2 HP

23. Most commonly used motor types in today’s industry is ........................

Induction motorAll of TheseDC motorSynchronous Motor

24. The direction of rotation of the induction motor can be reversed by.......

Changing all the three leads connection of the statorChanging the output connection of the statorChanging the connection in terminals star to delta & delta to starChanging any two leads connection of stator input

25. Rotor resistance starters are used with wound rotor induction motor When the motor is running the resistances in starter are.....................

Connected in deltaOpen circuitedConnected in starShorted