Pros & Cons of different trafo vector groups

[EPEngineer]

Hi everyone,
Could you please discuss the pros n cons and usage of different (most common) vector groups of distribution transformers including 2 wdg and three wdg e.g Dyn, Yyn, Ynynd, Ynynyn etc. Useful links are most welcome.
Thanks

 

[waross]

Do you have an application in mind?
Some schemes work fine with single transformers and are problematic with some configurations of three phase transformers.
Look at some of the threads on resistance grounding to get some idea of the grounding considerations.
There may be a saving in insulation costs for a transformer intended to be connected only in grounded wye as opposed to a similar transformer suitable for delta connection. A delta primary will better distribute an uneven load on a generator or system. A delta secondary or tertiary winding has issues with primary phase loss and/or primary voltage unbalance.
Search this site for harmonic mitigation. You should find descriptions of complimentary phase shifting connections used in an office building to mitigate harmonic currents.
yours

 

[EPEngineer]

Thanks waross,
I am involved in HV substation design so mainly the transformers I am interested in are the ones distributing loads to secondary or tertiary S/S or transformers. We have all sorts of consumers like industrial, domestic and commercial being supplied from the same transformer. So I am not able to think of any particular application. What can be the importance of S/S type like radial, double end fed and ring main S/S etc?
Is there any consideration of voltage level (like Transmission/sub tranmission and distribution level)for the selection of vector groups?

SMA

 

[waross]

There are several regular members on the site with more experience than I with substation design. I will butt out for awhile and see what the experts say.
respectfully

 

[RalphChristie]

For a start check:

http://www.beckwithelectric.com/powerlines/powerlines-37.html

for two-winding transformers.

I also recommend reading the J&P Transformer Book for aditional info.






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[EPEngineer]

Thanks RalphChristie,
It is indeed a helpful link.

SMA

 

[cuky2000]

Delta-Wye transformer connection is one of the most popular configurations in the power utility and industrial applications because this connection act as a natural isolation of the zero sequence component avoiding nuisance tripping of utility side for the most common faults such as phase to ground fault.

From the cost point of view, delta or any ungrounded transformer connections require full winding BIL. Therefore, the cost of the unit is more expensive.

Likewise, impedance grounded transformer also require higher BIL than grounded units.

For additional information on transformer connections see the image and links below.

[red]ADDITIONAL INFORMATION[/red]

http://cuky2000.250free.com/Zigzag_Data.gif

http://cuky2000.250free.com/Three_Winding_Transf.gif

 

[EPEngineer]

All I can say that is GREAT ...
Thanks

 

[ScottyUK]

WRT the last block of Cuky2000's table:

Generation applications typically use a dYN1 configuration as the GSU transformer with the generator connected at the LV delta and a high resistance earthing scheme (or transformer earthing scheme) applied at the generator star point. This is largely to allow limitation of generator earth faults to a mere handful of amps and save the hugely expensive stator core from severe damage in the event of an earth fault.

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