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something like wye-delta and delta-wye connection.

we can originally know wye-delta connection is step-down transformer and second side voltage phase is being to -30 degree. And also delta-wye connection is step-up transformer and second side voltage phase is being to +30 degree.

But the other side, we also can make wye-delta connection is step-up transformer if it get turn ratio like 1:2. So in this case maybe will be become +30 degree in second side voltage.

apply this principle in scott connection, how can work it?

case1) turn ration 1:2 - step up second side voltage's angle +90 degree?

case2) turn ration 2:1 - step down second side voltage's angle -90 degree?

if you have any information or homepage link, can you leave it for me?

thank you so much.

Chris Park
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  • Turns ratio has nothing to do with the phase shift. What is "scott connection"? – Andy aka Apr 29 '20 at 07:55
  • but i know that turn ratio can make step up and down environment. so maybe i know that it will make phase shift. is it right? – Chris Park Apr 29 '20 at 07:57
  • You ned to explain more clearly what you want to achieve. A Scott connection is intended to convert three-phase power to two phase. A specific ratio is required to achieve that. There is also a zig-zag connection that can provide a 15 degree phase shift for six phases. There is a specific ratio required for that also. There are other phase shifts that can be achieved, but if there are no applications for them, you will not find descriptions. –  Apr 29 '20 at 12:52

1 Answers1

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A wye-delta transformer can be configured so either side lags OR leads by 30 degrees. It does not matter which side is wye or delta or which side is higher/lower voltage. If it is an IEEE standard connected bank then the lower voltage side will lag the higher (C57.12.00-1987, 5.7.2).

Here is an example of wye-delta bank and a delta-wye bank in an ABC phase rotation system, connected so both low-side lags by 30 (i use lower case letters for low-voltage side). Notice that the 6 phase-neutral voltage phasors (the ones with only 1 subscript) have the exact same relationship in either case.

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I have never analyzed the Scott Transformer connection until tonight. Per this Wikipedia article it was developed to convert 3-phase to 2-phase in a balanced fashion (evenly loads the 3-phase system) as Charles mentions above. Below is my newly minted phasing derivation for this transformer arrangement. The key is to use KVL to calculate the voltage across the primary of the teaser - then rest of it falls nicely into place. Both transformers have N:1 ratio, but we are only using 86.6% of the top one.

Scott connection 3-wire

I hope this helps. I believe this answers your question about how the turns ratio used can affect the resulting phase shift on secondary - it clearly does in this connection. It is just all about scaling and adding/subtracting phasors.

Here is similar development for the variation of the Scott transformer to which you linked. They added a neutral connection in the Teaser for use on 4-wire system.

Scott 4-wire connecton

relayman357
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  • thank u so much and then can u discuss this issu with me? Can u see this link https://circuitglobe.com/scott-t-transformer-connection.html In this web site, u can see scott connection and then i wonder about this phase shift. V2t and V2m have a phase difference of 90 degrees. And V2t is leading of V2m. But if we give another turn ratio like a step up or step down, is it possible to replace the position like V2t is lagging of V2m? – Chris Park Apr 30 '20 at 04:05
  • Hi Chris - Recognize that you can simply roll polarity to the load connected to V12. This applies V21 which is 180 out of phase with V12. This V21 would lag V34 by 90 like you want. Also, look at the Vx phasor. It is created by adding the 1/2 of the VBC phasor to the VAB phasor. If you change the magnitude of either you will move the Vx phasor position. Note: I edited my answer to cover the 4-wire Scott you linked to. – relayman357 Apr 30 '20 at 13:30