Automatic Star / Delta Starter with Timer for 3-Phase AC Motors

In this tutorial, we are going to show the Star-Delta (Y-Δ) 3-phase induction AC Motor beginning technique by Automatic star-delta starter with Timer with schematic, power, management and schematic also as however star-delta starter works and their applications with blessings and drawbacks.

From the left you have got the most contractor with the gas timer as a result of your main contactor is often energized, within the Middle you have got the Delta contactor with a thermal overload for motor protection just in case the motor exceeds the ampere rating assault the thermal overload, on the proper you have got the Star contactor that is that the 1st contactor to be energized with the most contactor then once the timer reaches its cut-off date the Star contactor de-energizes and therefore the Delta contactor energizes and therefore the Motor is running at full load.

Operation & Working of Automatic Star Delta Starter

From L1 The section current flows to thermal overload contact through the fuse, then OFF push-button, On electric switch Interlocking contact two, and so C3. This way, the circuit is completed, as a result;

  • Contactor coil C3 and timer coil (I1) square measure energized promptly and also the motor winding then connected in Star. once C3 is energized, its auxiliary open links are going to be closed and the other way around (i.e. shut links would be open). so C1 Contactor is additionally energized and 3 section offer can reach the motor. Since winding is connected in Star, thus every section can get √3 times but the road voltage i.e. 230V. thus Motor starts safely.
  • The shut contact of C3 within the Delta line opens owing to that there would be no probability of activation of contactor two (C2).
  • After deed the electric switch, Timer coil and coil three can receive an offer through Timer contact (Ia), Holding contact three and also the shut contact two of C2.
    When Contactor one (C1) is energized, then the 2 open contacts within the line of C1 and C2 are going to be closed.
  • For the particular time (generally 5-10 seconds) within which the motor is going to be connected in star, after that, the Timer contact (Ia) are going to be open (we could amendment by rotating the timer knob to regulate the time again) and as a result;
  • Contactor three (C3) is going to be off, owing to that the open link of C3 is going to be closed (which is within the line of C2) so C2 will energize. Similarly, once C3 off, then the star affiliation of the winding will open. And C2 is going to be closed. Therefore, the motor winding is going to be connected to Delta. additionally,
  • Contact two (which is within the line C3) can open, by which, there wouldn’t be any probability of activation of coil three (C3)
    Since the motor is connected in Delta currently, therefore, every section of the motor can receive full line voltage (400V) and also the motor can begin to run fully motion.

Advantages & Disadvantages of Star Delta Starter with Timer


  • Simple style and Operation
  • Comparatively cheaper than different voltage dominant ways
  • Torque and Current performance of the Star delta starter area unit well.
  • It attracts twofold the beginning current of the FLA (Full Load Ampere) of the connected motor.
  • It reduced the beginning current to a common fraction (approximately) as compared to DOL (Direct ON-Line Starter)


  • Starting torsion additionally|is additionally} cut back to a simple fraction as a result of starter reduces the beginning current to simple fraction of the rated current [as Line voltage also reduced to fifty-seven (1/√3)]
  • It needed Six leads or terminals Motor (Delta Connected)
  • For Delta affiliation, the provision voltage should be an equivalent because of the rated motor voltage.
  • At change time (From Star to Delta), if the motor doesn’t reach a minimum of ninetieth of its rated speed, then the present peak could also be equally high as in Direct ON-Line starter( D.O.L), therefore it should cause harmful effects on the contacts of the contractor, thus it might not be reliable.
  • We might not use star delta starter if the desired (application or load) torsion is quite five-hundredths of the three-phase induction motors rated torsion.

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