# star delta

Discussion in 'Electrics UK' started by markymark2406, 8 Sep 2007.

1. ### markymark2406

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whats the fifference between a star and delta motor and why?

2. ### ricicle

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The subject of motors can be quite involved.Basically most 3 phase induction motors have 3 windings.In the majority of them these winding 'ends' are brought out into the terminal box.If you look at the rating plate it will tell you which configuration to use.Most will be designed to run at 415V in Delta, however this can lead to high start up currents due to the max. voltage being applied when the motor is stationary and there is no oppostion to current flow.This can be overcome by reducing the voltage across each winding by connecting them in Star.
However the disadvantage of this is that you have reduced the starting torque of the motor and may prove a problem in some applications.

If you can imagine the windings are called A, B and C.So winding A will have 2 ends A1 and A2 etc.Connection in Star means that A2, B2 and C2 are connected together and 3 phase is applied to A1, B1 and C1.
For Delta connection A1,C2 are together, as are A2, B1 and B2, C1.3 phase is applied to each of these pairs.
Older Star/delta starters were manual, but more recent ones are automatic, the changeover time between Star/Delta operation being determined by how the load reacts.

Hope this helps.

3. ### Space cat

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I find that a diagram saves a thousand words. The only trouble is that I don't know how to post diagrams here!

Delta is the fourth letter of the Greek alphabet and the upper case symbol is a triangle (but maybe you knew that already). Draw yourself a triangle with all sides equal and then put a dot right in the centre. Now draw three lines out from this dot to the triangle's vertices. That's the star. For a delta connected motor the windings are in the three sides of the triangle; for star connection they are in the three arms of the star.

This is more than just a wiring diagram because the lengths of those lines represent voltages and their angles are the phase angles. If each side of your triangle is 415 volts then the three arms of the star are, very nearly, 240 volts. You can check this using trigonometry or careful measurement on a scale diagram.

On a star connected three phase supply the centre dot is neutral but you don't need to make this connection on the motor because the currents in the three arms of the star add up to zero.

4. ### markymark2406

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It would be good to see diagrams of these, any chance?

5. ### davy_owen_88

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Space cat, have a look through this thread for information on how to upload and insert a picture into your post.

If the image is already uploaded then you just have to copy the address for the image and put IMG tags around it like this:

6. ### Space cat

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Thanks davy. I'll study that next time I'm properly awake.

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8. ### empip

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http://cda.org.uk/Megab2/elecapps/elec_hom.htm

http://cda.org.uk/Megab2/elecapps/elec_hom.htm

http://cda.org.uk/Megab2/elecapps/elec_hom.htm

9. ### markymark2406

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Just confirm someone the links you put in the connection box on the motor? in star i know that you linkout one side UVW but what about delta?

10. ### ricicle

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U1-W2, U2-V1, V2-W1

11. ### markymark2406

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still not clear, can you draw or direct me to a website with pictures?

12. ### ricicle

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Have you checked on the inside of the terminal box cover - there is usually a diagram in there?

There should be 6 studs - U1 U2, V1, V2, W1, W2

It should be possible to fit a link between U1+W2, a link between U2+V1 and a link between V2+W1.

This normally creates 3 parallel links.You then wire ONE incoming phase to each of these links.

If you still don't understand I suggest you read up before you undertake this kind of work.

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