Ppt

2. Need of starter
A 3 Phase Induction Motor When Started From Rest
It Is Act As A Short Circuited Of Transformer.
When The stator Of 3 Phase Induction Motor Is
Connected To The Rated Voltage Motor Draw (Tech)
A Heavy Current Which May Damage The Motor If It
Is Slow For Long Time.

3.  Stator resistance starter
 Auto transformer starter
 Star-delta starter
 Rotor resistance starter
 Direct on line (DOL) starter
TYPES OF STARTER

4. STATOR RESISTANCE STARTER

5. A starter resistance is connected in each line in series with each
phase winding of the stator.
Initially all the starter resistance are kept in “Start” position so
that they offer their maximum resistance .
The switch is turned ON to connect the three phase AC supply
to the stator winding.
Due to starter resistance in series, each phase winding will
receive a reduced voltage. Due to reduction in the value of V1 , the
starting current is limited to a safe value.
As the motor accelerates, the starter resistance is reduced by
moving the variable contact of the resistance towards the “Run”
position.
In the “Run” position, the starter resistance is shorted out and
full stator voltage is applied across the stator winding.

6. . AUTO-TRANSFORMER STARTER
An autotransformer is used to apply a low voltage to the stator winding
at the time of starting. When the motor speed reaches the desired level,
autotransformer is disconnected and motor is connected directly across
the supply.
 The stator of the motor is connected through a 6-way double throw
switch.
 While starting, the switch is thrown to ‘Start’ side so that a reduced
voltage is applied to stator. This keeps the starting current safe limits.
 Once motor take up the speed, the switch is throw to ‘Run’ side so
that full supply voltage is applied to stator.
 A specific advantage of this starter is that reduction in voltage during
starting, can be done to any desired level by selecting proper tapping
of the autotransformer.

7. Diagram

8. ROTOR RESISTANCE
STARTER

9.  This starter is used with a wound rotor induction motor. It
uses an external resistance/phase in the rotor circuit so that
rotor will develop a high value of torque.
 High torque is produced at low speeds, when the external
resistance is at its higher value.
 At start, supply power is connected to stator through a three
pole contactor and, at a same time, an external rotor
resistance is added.

10. The high resistance limits staring current and allows the motor to
start safely against high load.
Resistors are normally of the wire-wound type, connected through
brushes and slip rings to each rotor phase. They are tapped with points
brought out to fixed contactors.
As the motor starts, the external rotor resistance is gradually cut out
of circuit ; the handle or starter is turned and moves the three contacts
simultaneously from one fixed contact to the next.
The three moving contacts are interconnected to form a start point
for the resistors.

11. Star Delta Starter
 Most induction motors are started
directly on line, but when very
large motors are started that way,
they cause a disturbance of voltage
on the supply lines due to large
starting current surges.
 To limit the starting current surge,
large induction motors are started
at reduced voltage and then have
full supply voltage reconnected
when they run up to near rotated
speed.

12. D.O.L.(direct on line) starter

13. AStarter Which Connects A Motor Directly
Across The Line Is Called D.O.L. Starter.
In This Method, The Motor Is Connected By
Means Of A Starter Across The Full Supply
Voltage.
It Is V
ery Simple, Inexpensive, Easy To InstallAnd
Maintain.
It Consist - START Button
- OFF Button
- Overload Relay
Switching By This Starter Is Directly From Line
WithoutAny Provision To Control The Starting Current
i.e. There Is No Device To Reduce The Starting Current
In This Starter.

14. Comparison Of Different Staters
Sr.no Types Of
Starter
Line
Voltage
Applied
Starting
Current
Starting
Torque
Produce
Specially Drawbacks The
Starter
1 Dol Starter Full Voltage
100%
About 6
Time F.L
Current
Twice Is
F.L
Torque
1. Simple
2. Cheaper
3. Good Starting Torque
2 Star Delta
Starter
57.7% About
Twice The
F.L
Current
2/3 Of F.L
Torque
1. Simple
2. Cheaper
3. For Low Capicity Motors
Up To 30 H.P
3 Auto
Transformer
40% 3.84
Times F.L
Current
1.28
Times F.L
Torque
1. For Higher Capicity
Motor Above 30 H.P
2. Cost Is Very High
3. Reduction Is Starting
Torque

15. 4 Stator
Resistance
Starter
50% 2 Times F.L
Current
0.25 Times
F.L Torque
1. For Low
Capicity
Motor
2. Cost Is
Cheaper
5 Rotor
Resistance
Starter
Full 2 Times F.L
Current
2 Times F.L
Torque
1. For High
Capicity
Motor
2. Oil
Immersed
Costly

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