Browse products from Schneider Electric - WW in Star delta starter for TeSys D and reversing contactors are available from 9 A to A (inductive motor), and. Closing the ON push-button switch actuates the main magnetic contactor, the star contactor, and the timer, while leaving only the delta. Above diagram shows V1 and V2 connected to same phase through the main contactor and delta contactor. But,This diagram is wrong.


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Star-delta starters are particularly suited for high inertias, where the load are initiated after full load speed. The motor is started in Y-connection and accelerated and switched to the star-delta connection.

How do direct-on-line (DOL) and star-delta motor starting compare?

This method can only be used with induction motors that are delta connected to the supply voltage. If the changeover from star to delta takes place at too low a speed, this can cause a current surge star delta motor starter rises almost as high as the corresponding DOL value.

During the even small period of switch over from start to delta connection the motor looses speed very rapidly, which also calls for higher current pulse after connection to delta.

This sequence happens in a friction of time. After pushing the ON push button switch, the auxiliary contact of the main contactor coil 2 which is connected in parallel across the ON push button will become Star delta motor starter to NC, thereby providing a latch to hold the main contactor coil activated which eventually maintains the control circuit active even after star delta motor starter the ON push button switch.

Now Motor terminal connection change from star to delta connection. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active. The control circuit above also provides two interrupting contacts to shutdown the motor.

Star Delta Starter

The OFF push button switch break the control star delta motor starter and the motor when necessary. The thermal overload star delta motor starter is a protective device which automatically opens the STOP Control circuit in case when motor overload current is detected by the thermal overload relay, this is to prevent burning of the motor in case of excessive load beyond the rated capacity of the motor is detected by the thermal overload relay.

At some point during starting it is necessary to change from a star connected winding to a delta connected winding. Power and control circuits can be arranged to this in one of two ways — open transition or closed transition. What is Open or Closed Transition Starting 1.

What is Star Delta Starter? - its theory - Circuit Globe

Open Transition Starters Discuss mention above is called open transition switching because there is an star delta motor starter state between the star state and the delta state. In open transition the power is disconnected from the motor while the winding are reconfigured via external switching.

When a motor is driven by the supply, either at full speed or at part speed, there is a rotating magnetic field in the stator.


This field is rotating at line frequency. Star delta motor starter flux from the stator field induces a current in the rotor and this in turn results in a rotor magnetic field. When the motor is disconnected from the supply open transition there is a spinning rotor within the stator and the rotor has a magnetic field.

Due to the low impedance of the rotor circuit, the time constant is quite long and the action of the spinning rotor field within the stator is that of a generator which generates voltage at a frequency determined by the speed of the rotor.

When the motor is reconnected to the supply, it is reclosing onto an unsynchronized generator and this result in a very high current and torque transient.

The magnitude of the transient is dependent on the phase relationship between the generated voltage and the line voltage at the point of closure can be much higher than DOL current and torque and can result in electrical and mechanical damage.

Open transition starting is the easiest to implement star delta motor starter terms or cost and circuitry and if the timing of the changeover is good, this method can work well.