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Why is starter necessary for a three-phase induction motor?
 Question Submitted By :: Electrical-Engineering
I also faced this Question!!     Answer Posted By  
# 1
A starter is needed for a three phase induction motor
because at the time of starting, if induction motor is
started directly, it will draw large amount of current
which causes damage to adjoining equipments.
Thus, a starter is needed in order to limit the starting
current.After the motor has started at reduced starting
current and hence reduced voltage, the connections are
diverted towards the mains supply so that now, the motor
can run at higher starting current and voltage.
Four types of starting methods are employed:
2.Auto transformer method
3.Primary resistor starting.
4.Direct On-line.
Low rating upto 7 H.P motors can be started directly.
Is This Answer Correct ?    194 Yes 9 No
# 2
By starting an induction motor with starter limits the
starting current and starting torque .

Note - Upto 5 to 7.5 HP Three phase induction motors
generally started direct on line .
Is This Answer Correct ?    180 Yes 28 No
# 3
Is This Answer Correct ?    119 Yes 37 No
G.v.suresh Kumar
# 4
The starters are used to limit the starting current to
accepteble value.
Is This Answer Correct ?    84 Yes 9 No
# 5
at the time of starting slip S= 1, so the rotor resistance
which depends on slip i.e.
R2(1-S)/S will be equzl to "0",
i.e. rotor will act as short circuit.
hence initailly motor will draw heavy amount of current.
So in order to reduce this inrush current(5 to 7 times of
rated current), we apply less input voltage at the time of
starting so that input curent will be low(as in case of
star connection) & after some time or specified time input
will be fed in Delta connection.

if u understand this then ok other wise read more books in
Is This Answer Correct ?    76 Yes 9 No
# 6
1--it limit the starting current.
2--increase the starting torque.
Is This Answer Correct ?    61 Yes 24 No
# 7
Starter is used to reduce starting current.starting current
is usually large because of inertia,charecteristics of
motor winding(at starting slip=1,rotor resistance low
implies less back emf).So at starting we use starter .for
example.STAR DELTA using a starter at least the
switching is improved which is much important for safe and
longer life time use.simply a DOL can be used for lower
rated motors (up to 07 HP)in this case.for higher rated
motors (up to 15 HP)we can use a star delta connection.a
delta connected motor takes 1.7 times line current than a
star connectd motor.think ! at starting the current is
almost halved .Now a days we use drives (power electronics
products which not only takes care of starting of a motor
(improving power factor) also controls it as perrequirement.
Is This Answer Correct ?    38 Yes 4 No
# 8
starter is reqired for the purpose of reduce starting
current. starting current reduce in starting period so that
starting torque is increase. another thing is that if
starter is not provided than high amont of current flow in
starting beacuase of that it may be chances to damege
itself and alose its adjoining m/c.
Is This Answer Correct ?    34 Yes 14 No
Bhavik Parekh
# 9
starter is required to limit the high starting current 
Is This Answer Correct ?    26 Yes 6 No
# 10
when the induction motor starts.slip i.e "s" has a value
1...and hence the internal resistance value becomes
0..since resistance is directly proportinal to (s-1)
the resistance becomes 0..according to ohms law current
becomes very high.....tha value of current is about 5 to 6
times the full load curent......therefore the motor must
accelerate to high speed ,,which is not possible at "load"
condition.....and hence the motor may burst due to prevent the motor from bursting
by reducing the value of current we use a STARTER....
Is This Answer Correct ?    16 Yes 5 No
Monika Khatri

Other Electrical Engineering Interview Questions
  Question Asked @ Answers
why lightning arrester and other equipment earthing conneting from same earth bar ?   1
If single phase voltage level is 230V than why three phase voltage level is not 660V ?, but it is only 440V. TCS 12
What is mean by sink and source in term of PLC and drives,where and how they used in logic   2
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In Siemens S7-300 PLC, what is funtion and funtion block ? What is the difference between them ? When to use function and when to use function block   2
For a load of 40HP induction motor.what will be size of Armoured copper cable require to connect the motor to starter in Star-Delta? CG 1
In a three phase transformer(delta/star connected)when i touch one end of the bulb in any one phase and other end to earth..will the bulb glow or not..if not why?..i'm touching the bulb in star connected side...   5
When we are working on transformer(132\11KV). we are going to isolate the transformer from both HV side and LV side. then we are applying grounding on both side. My question is that we required to isolate the VT which is still connected from secondary side.?   1
cost of operation of which plant is least?   6
how to calculate the powerfactor in induction motor having name plate details? for example 1 h.p motor 1.86 A 415 V   6
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How the flights will be fly be fly without ground connection under raining with thunder lighting?   1
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