Star delta starter circuit for protection of motor

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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