Star delta starter circuit for protection of motor

1. Welcome to our
Presentation

2. Presented By:
Md. Arifuzzaman Sunny
162-33-3500
Md. Atikul Islam Ashik
162-33-3507
Submitted to:
Kanij Ahmad
Department of EEE
Daffodil International University

3. Performance of a Star-
Delta Starter Circuit
for the protection of
Motor
TOPIC

4. Star-Delta Starter
The Star/Delta starter is manufactured from three
contactors, a timer and a thermal overload. The
contactors are smaller than the single contactor used in a
Direct on Line starter as they are controlling winding
currents only. The currents through the winding are
1/root 3 (58%) of the current in the line.

5. Power Circuit of Star- Delta Starter

6. Control Circuit of Star-Delta Starter

7. In that circuit when Start button is pressed Star and Main contactor gets holds
and motor get started in Start connections and after certain delay which was
set in timer star contactor get disengage and delta contactor comes in line.
Star and Delta contactor NC’S are take in line both in Delta and contactor line
so that only 1 contactor either star or Delta may comes in line.
In Star Delta Starter since Six leads goes at Motor end so in each lead phase
current will flow so Overload relay used for Star-Delta circuit is usually for
phase current not line current.

8. Working Principle of Star-Delta Starter
 High Starting Current
Starting current = 7 x full load
current
As speed increases, stator current
reduces

9. Working Principle of Star-Delta Starter
Start off in STAR, then run in
DELTA
Motor current follows STAR curve.
Change over to DELTA curve after
motor reaches 80% of full
synchronous speed Change over can
be done using a timer or centrifugal
switch

10. Working Principle of Star-Delta Starter
Start off in STAR, then run in
DELTA
Motor torque follows STAR
curve. Change over to DELTA
curve after motor reaches 80%
of full synchronous speed
Lower starting torque in STAR
means that load must be
checked to ensure it can be
turned in STAR.

11. Applications of Star-Delta
Starter
In a cage induction motor, the starter is used only to decrease the input voltage to the
motor so as to decrease the starting current. It is T.P.D.T switch used to first start the motor
with the winding connected in star and then switch for delta connection in running
position.
In most of industries for motors above 7.5 KW star-delta starters are used. Star-delta
starters are used as during starting start current get reduced bye 1/3 times and also torque
get reduced by 1/3 times.

12. Why is star delta starter preferred
 Star Delta Motors are preferred as a method of starting in Low starting Torque
Applications. The starting current of Induction motors are six to seven times the full
load current. Starters are employed to reduce the starting current.
 A star Delta Starter reduces the starting current by connecting the motor winding in
Star at the time of starting. This reduces the voltage across the winding . The
voltage across the winding will be( 1/√ 3)*Line Voltage.
 After the starting time set in the timer the winding will be connected in Delta. The
voltage across the winding will be equal to the line voltage.
 The switching of winding configuration is done by devices called contactors. Typical
application of Star Delta motors are compressors

13. Advantages
 The operation of the star-delta method is simple and rugged
 It is relatively cheap compared to other reduced voltage methods.
 Good Torque/Current Performance.
 It draws 2 times starting current of the full load ampere of the motor
connected

14. Disadvantages
 Low Starting Torque (Torque = (Square of Voltage) is also reduce).
 Break In Supply – Possible Transients
 Six Terminal Motor Required (Delta Connected).
 It requires 2 set of cables from starter to motor.

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Presentation
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