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Star Delta (Y-Δ) Starter For Automatic 3-Phase Motor

Automatic Star / Delta (Y-Δ) Starter with Timer for 3-Phase Motor

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

Automatic Star Delta Starter with Timer Wiring & Installation Diagram

Automatic Star Delta Starter with Timer Wiring Diagram
Automatic Star Delta Starter with Timer For Three Phase Motor

Explanation of the working and operation of Star Delta Automatic Starter with Timer Wiring Installation:

From the left you have the main contactor with the pneumatic timer because your main contactor is always energized, in the Middle you have the Delta contactor with a thermal overload for motor protection in case the motor exceeds the ampere rating set on the thermal overload, on the right you have the Star contactor which is the first contactor to be energized with the main contactor then when the timer reaches its time limit the Star contactor de-energizes and the Delta contactor energizes and the Motor is running at full load.

Related Motor Control & Power Diagram

Operation & Working Principle of Star Delta Automatic 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;
  • 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 of Star Delta Automatic Starter

Click image to enlarge

Star Delta 3-phase Motor Automatic starter with Timer Power Circuit Diagram:
Star Delta 3-phase Motor Automatic starter with Timer Power Circuit Diagram

Control Circuit Diagram of Star Delta Automatic Starter with Timer

Click image to enlarge

Star Delta 3-phase Motor Automatic starter with Timer Control Circuit Diagram:
Star Delta 3-phase Motor Automatic starter with Timer Control Circuit Diagram

Abbreviations: ( FOR Control Wiring of Three Phase Star Delta Starter with Timer)

  • R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
  • C.B = General Circuit Breaker
  • Main = Main 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)

Related Posts:

Advantages of Star Delta Automatic Starter with Timer

  • 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 Star Delta Starter with Timer

  • 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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  1. 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….

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

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

  4. 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

  5. I once worked on a Large Burnt out 3 Phase Motor which was used for pumping sugar from the delivery Road Tanker Lorry into a Sugar Storage Tower Silo. My boss told me the windings were unusual because they were of a STAR STAR DELTA configuration ?

    Have you come across this type of motor windings arrangement before ?


    Norman Peoples

  6. Plz send me working principle and construction of semi automatic star delta starter….
    I can’t understand reletade website information….

  7. Plz send me working principle and construction of semi automatic star delta starter….
    I can’t understand reletade website information….

  8. Hi, I have this winding automatic STAR DELTA with timer and the inverter (Hz) to operate the 3 phase motor at my workplace.
    Recently we have facing the motor was tripped and error shown at inverter display is “L In”, sometimes “OL”, sometimes”L U”, and “OV1” when tripped.
    Could someone advice how to troubleshoot this problem?

    Thanks Best Regards.

  9. I think In the actual built circuit shown as picture posted, the star contactor is connected to the thermal overload terminal from motor side, which is more safety may be, not from delta contactor side as shown in power circuit diagram.

    Thanks for your valued information, it realy helped me alot.

  10. thanks for your schematics
    i made the start delta control circuit in fluid-sim, and i releized that it repeat the cycle when you press the start button again, and as solution i suggested to energize the main contact first.

    1. Wiring connection reference will be near the terminal box of motor or the terminal box cover. This circuit is concept of star start delta run motors. Main supply will be connected to U1, V1, W1 and the configuration of star or delta will be based on the active contactor. Timer is to delay the turning off of the star contactor and delaying the turning on of the delta contactor. But what if the voltage of start is different from the run voltage?

  11. Please inform me have any Dealer of Automatic Star Delta Starter for 10Hp motor pump in Kolkata market? Give me address and contract no.

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