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The Star-Delta (Y-Δ) 3-phase Motor Starting Method by Automatic star-delta starter with Timer.

The Star-Delta (Y-Δ) 3-phase Motor Starting Method by Automatic star-delta starter with Timer.

Abbreviations: ( FOR 3-phase Motor Starting Method by Automatic star-delta starter)

R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
C.B = General Circuit Breaker
Main = Mai Supply
Y = Star
Δ = Delta
1a = Timer
C1, C2, C3 = Contatcors (For Power & Control Diagram)
O/L = Over Load Relay
NO = Normally Open
NC = Normally Closed K1 = Contactor (Contactor coil) 

K1/NO = Contactor Holding Coil (Normally Open)

Operation and Working Principle of Automatic Star Delta Starter:

From L1 The phase current flows to thermal overload contact through Fuse, then OFF Push button, On Push button Interlocking Contact 2, and then C3. This way, the circuit is completed, as a result;

  1. Contactor coil C3 and Timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and vice versa (i.e. close links would be open). Thus C1 Contactor is also energized and Three Phase Supply will reach to the motor. Since winding is connected in Star, hence each phase will get √3 times less than the line voltage i.e. 230V. Hence Motor starts safely.
  2. The close contact of C3 in the Delta line opens because of which there would be no chance of activation of contactor 2 (C2) .
  3. After leaving the push button, Timer coil and coil 3 will receive a supply through Timer contact (Ia) , Holding contact 3 and the close contact 2 of C2.
  4. When Contactor 1 (C1) is energized, then the two open contact in the line of C1 and C2 will be closed.
  5. For the specific time (generally 5-10 seconds) in which the motor will be connected in star, after that the Timer contact (Ia) will be open (We may change by rotating the timer knob to adjust the time again) and as a result; 

Also read; 
(I) Starting & Stopping of 3-Phase Motor from more than One Place Power & Control diagrams
(ii) (ON / OFF Three-Phase Motor Connection Power & Control Schematic and Wiring Diagrams)

  • Contactor 3 (C3) will be off, because of which the open link of C3 will be close (which is in the line of C2) thus C2 will also energize. Similarly, When C3 off, then star connection of winding will also open. And C2 will be closed. Therefore, the motor winding will be connected in Delta. In addition, Contact 2 (which is in the line C3) will open, by which, there would not be any chance of activation of coil 3 (C3)
  • Since the motor is connected in Delta now, therefore, each phase of the motor will receive full line voltage (400V) and the motor will start to run in full motion. 

Also Read;

  1. Main Difference between contactor and Starter. 
  2. A simple circuit diagram for understanding the Working of contactor.
  3. Why We Need to Install a Starter with a Motor?

 Power Circuit Diagram:

Click image to enlarge
Automatic Star delta Power Control Diagram

 

Control Circuit Diagram:

Click image to enlarge

 

Star Delta Starter Control Diagram

 

Advantages of Automatic Star Delta Starter

  • Simple Design and Operation
  • Comparatively cheaper than other voltage controlling methods
  • Torque and Current performance of the Star delta starter is well.
  • It draws two times starting current of the FLA (Full Load Ampere) of the connected motor.
  • It reduced the starting current to one-third (approximately) as compared to DOL (Direct ON Line Starter) 

 Also read:

  1. Three Phase Motor Connection Reverse and Forward Power and Control wiring diagrams
  2. Two Speeds One Direction Three Phase Motor Connection Power and Control Diagrams
  3. 2 Speeds, 2 Directions Multispeed 3-phase Motor Power & Control Diagrams

Disadvantages of Automatic Star Delta Starter

  • Starting Torque is also reduce to one-third because starter reduce the starting current to one-third of the rated current [as Line voltage also reduced to 57% (1/√3)]
  • It required Six leads or terminals Motor (Delta Connected)
  • For Delta connection, the supply voltage must be same as the rated motor voltage.
  • At switching time (From Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in Direct ON Line starter( D.O.L), thus it may cause harmful effects on the contactors contacts, so it would not be reliable.
  • We may not use star delta starter if the required (application or load) torque is more than 50% of the three phase induction motors rated torque

You may Also Read Other Power & Control Diagrams here:


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13 comments

  1. Its very usefully circuits .

  2. Its very usefully circuits .

  3. should be use one more timer for disconnect Main and Star contactor … if delta contactor faulty. its very importend.<br />

  4. It&#39;s very inportant circuit for industrial aria

  5. It&#39;s very inportant circuit for industrial aria

  6. i also have diagram but how can i sent it to u…but may be this one helps u star connection is A1 B2 C3 close the other ends and for delta connect A1 B2 , B1 C2 , C1 A2….

  7. i want about how to calculate a resistor.<br />

  8. What is the use of timer in this circuit and how will delta operate after a delayed timing? plz analyse ur circuit once again

  9. Please Describe the the control circuit diagram of Automatic Star Delta Starter with Timer for 3-phase Motor

  10. Need ckt diagram fr three motor having star delta starter on same mcc such that only 2motor can start simultaneously not 3rd one

  11. the timer in the circuit is used to time out c3 and time in c2 .to understand it just identify the contact of the timer in the circuit .u will see one contact is closed for c3 and one open for c2

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