Star delta starter
This is a starting method that reduces the starting current and starting torque. The device normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position).
The motor must be delta connected during a normal run, in order to be able to use this starting method.
The received starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start.
This starting method only works when the application is light loaded during the start. If the motor is too heavily loaded, there will not be enough torque to accelerate the motor up to speed before switching over to the delta position.
Description of Operation
To enable the motor to start, the motor windings are configured in a star formation to the supply voltage.
The voltage applied to the individual motor windings is therefore
reduced by a factor of 1√3 = 0.58 this connection amounts to approximately 30% of the delta values. The starting current is reduced to one third of the direct starting current.
Due to the reduced starting torque, the star-delta-connection is suitable for drives with a high inertia mass but a resistance torque which is low or only increases with increased speed. It is preferably used for applications where the drive is only put under a load after run-up.
After motor run-up, in most cases an automatic timing relay controls the switch-over from star to delta. The run-up using star connection should last until the motor has reached the approximate operational speed.
so that after switching to delta, as little post acceleration as possible is required. Post-acceleration in delta connection will instigate high currents as seen with direct on-line starting.
The duration of start in star connection depends on the motor load. During delta connection, the full mains voltage is applied to the motor windings.
To enable a switch-over from star to delta, the six ends of the motor winding are connected onto terminals. The contactors of a star-delta starter switch over the windings accordingly.
How it works?
Starting in star, the main contactor connects the mains to winding endings U1, V1, W1.
The star contactor shorts winding endings U2, V2, W2.
After successful run-up, the star contactor switches itself off and the delta contactor connects terminals U1/V2, V1/W2,W1/U2.
When changing from star to delta, attention has to be paid to the correct phase sequence.Incorrect phase sequence can lead to very high current peaks during the cold switch-over pause, due to the easy torque reduction following re-start.
These peaks can damage the motor windings and stress the control gear unnecessarily. The rotation of the motor has to be considered as well.
For star delta wiring technique and motor termination,Please read my post for star delta motor connection.Also for simple star delta control circuit wiring and types of star delta starter,please refer to my post for Electro mechanical star delta.
For more detail,please refer to ELECTRIC MOTOR HANDBOOK :-
Good informations in this site. how to to find out the wrong termination in star delta connection. for example in star delta connected motor star in star mode but after change in delta mode contactor of delta and main are in pick up condition but motor got off not in trip. can u explain this
Are u already confirm your motor connection true or not?i think your motor terminal connection maybe wrong..please refer my last post about star delta motor connection
please give a diagram of star-delta starter with transition resistors(Kondorfer)
please refer to my post : http://www.electricneutron.com/motor-control/electro-mechanical-star-delta-starter/
hi,
The artical which is above is more enough to understand and knowledge of particular thing.
very usefull
plz send to my email a control circuit of forward reverse connection…A.S.A.P….thank you…
i will discuss in my next post about control circuit of forward reverse for star delta starter…thanks
can anyone tell me about the difference in delta and star connections from the generator?
please post me the book to my email,thank you.
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in a star delta stater how we can set the timer timing to switch to delta from star according to load characterstics.
it hard to setting the best timing for star delta starter.Typical setting for timer is around 8 until 10 second….
Dear Sir,
We are manufacturer of animal food.it is in pallate fome.and our requirement of Star-Delta Starter for 40HP Motor.so,please give the Quotation for the same.
Kind Regards,
Chandrakant Parekh.
+91 95588 13099
Director
Divine Ani-Food Manufacturing Unit.
Unjha(Mehsana)