Browse  |   Placement Papers  |   Company  |   Code Snippets  |   Certifications  |   Visa Questions Post Question  |   Post Answer  |   My Panel  |   Search  |   Articles  |   Topics  |   ERRORS new

 Categories >> Engineering >> Electrical Engineering

 Civil Engineering Interview Questions (3072) Mechanical Engineering Interview Questions (3287) Electrical Engineering Interview Questions (13323) Electronics Communications Interview Questions (2362) Chemical Engineering Interview Questions (416) Aeronautical Engineering Interview Questions (77) Bio Engineering Interview Questions (17) Metallurgy Interview Questions (79) Industrial Engineering Interview Questions (163) Instrumentation Interview Questions (2375) Automobile Engineering Interview Questions (106) Mechatronics Engineering Interview Questions (38) Marine Engineering Interview Questions (43) Power Plant Engineering Interview Questions (75) Engineering AllOther Interview Questions (1195)
Question
```what is the difference between induction and synchronous
motor?explain in simple words?why 3 phase motor is given
preference over single phase motor.```
Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By

# 1
Following are the differences between an induction and
synchronous motor:
1. An induction motor is singly excited motor (i.e.)power
supply is fed only to the stator. On the otherhand, a
synchronous motor is doubly excited (ie) stator must be
supplied from an ac source while the rotor is supplied from
a dc source.
2. An induction motor can only run at speed less than the
synchronous speed. While a synchronous motor can run only
at synchronous speed.
3. A 3phase induction motor is self starting while the
synchronous motor is not self starting (i.e.)it has to be
driven by another motor upto or near synchronous speed
before being pulled-up by the synchronously rotating flux
(magnetic locking).
4. In an induction motor Stator has field windings and the
rotor is the armature. In a Synchronous Motor, the field
winding is the Rotor while armature is the Stator

The relationship between frequency and speed is given by

f=pn/120 ; where f = frequency, n = speed,
p = no. of poles

For a 4 pole motor supplied from 3 phase 50Hz power supply,
the speed would be 1500rpm. This speed is called
synchronous speed. This means that the speed of induction
motor will always be less than 1500rpm whereas the
synchronous motor can run only at 1500rpm.

3phase machines are used for high power applications
usually of about 1kW whereas 1phase motors are used for
fractional horse power applications.

3phase induction motors are self starting whereas 1phase
motors are not self starting but can be made self starting
by temporarily started as 2phase motor having two windings
using capacitors for one phase.

 Is This Answer Correct ? 39 Yes 1 No
M S Kumar

# 2
The main diffrence betwwen synchronous Moter & Induction
motor is.(On Designing Basis)..In the inductoin motor field
winding is on Stator & armature winding is on Rotor While
in Synchronous Motor the Field winding is on on Rotor &
Armature winding is on Stator

 Is This Answer Correct ? 42 Yes 13 No
Tarkeshwar Mall

# 3
the induction motor run at lower than synchorous
speedsynchorous synchorous speed.

 Is This Answer Correct ? 37 Yes 14 No
Amirtha

# 4
Synchronous motor : doubly excited (DC to the rotor , AC to the stator), not self starting , high PF (used as capacitor bank) , unity or leading PF , high efficiency (low inrush current) , Shorter operational life compared to the induction motor (brushes).

Induction motor : singly excited (AC to the stator), self starting , low PF , lagging PF , low efficiency (high inrush current) , longer operational life compared to the Synchronous motor (no brushes).

 Is This Answer Correct ? 11 Yes 0 No
Mohammed Subhi Assaf

# 5
the diffrence is comes at their speeds.
IM runs at iess than synchronus speed
sm runs at synch speed

 Is This Answer Correct ? 13 Yes 4 No
Upendra

# 6
Synchronous motor working as a leading power factor and
induction motor working lagging power factor. synchronous
motor used for power factor improving.

 Is This Answer Correct ? 11 Yes 2 No
Mukesh Kumar

# 7
IM is a self start motor while synchronous motor is not
self start.

 Is This Answer Correct ? 9 Yes 1 No
Shanawaz

# 8
induction motor has self starting torque. synchronous motor
has no self-starting torque therefor some external means be
used to start it.

 Is This Answer Correct ? 7 Yes 1 No
Sharvan Kumar Saini

# 9
main difference is that why IM doesnt run at synchronous speed?
coz of the slip.
ns= 120F/P
slip=(ns-1)/ns at synchronous speed

at standstill condition slip (%)will be 1
so as the slip increases speed of the motor decreases.

slip in the case of IM at standstill condition is 1. so
obiviously IM wont run at synchronous speed.

 Is This Answer Correct ? 6 Yes 1 No
Hrishikesh

# 10
synchronous motor is also for power factor
improvement.while induction motor not

 Is This Answer Correct ? 5 Yes 0 No
Suraj

  Question Asked @ Answers Other Electrical Engineering Interview Questions tell me the operation of ELCB. How it detects a fault? 4 Dear Sirs, I am a technical persons.In one of our Electrical Sub- Station, We have installed three numbers of 1250KVA ,11KV/0.415KV Transformer to feed the Factory load. We have found some abnormality. In one of our Transformers the leakeage current from transformer body to earth through earth continuity wire is almost 86 Amp but in other transformer it is (5-10)Amp. where the load current on three phase and neutral are respectively 1360Amp,1400Amp,1370 Amp & 176Amp. So please any technical person help me about the reasons of this situation and how I can rectify the fault. Moreover,I have measured the earth resistance of the Earth continuity wire which is less than 1 Ohm. Thanks Tapas Barua 2 Why used in layer by layer charcoal and salt used in earth pits. HP 7 WHAT SHOULD BE THE MINIMUM IR VALUE FOR LV (380V) CABLES ACCORDING TO IEC/IEEE. 3 I know during Surge Impedance Loading maximum power is transferred through a transmission line and also Sending end voltage becomes equal to Receiving end voltage i.e Vs=Vr so my question is if both end voltages are equal then how current travels in such line hence how power is transmitted because flow of current needs Potential difference?? NTPC 3 WHY 6.6KV MOTORS ARE STAR CONNECTED AND WHY NOT DELTA CONNECTED, Bhel 15 In winter we seem lightly an electric shock when we touch to doors(sometime) Infosys 13 How can we define 'Phase' 3 what is derating?, why it is neccesary, it is same for all means for drives, motors,and cables. 1 Hp to Kw and Kw to I(amps) conversion...... 3 How to check op amp using multimeter 1 What is rated value? is it phase values or line values? 1 For more Electrical Engineering Interview Questions Click Here