Transformer Selection and Reducing Fault Contribution 2

[Energyfit24381]

Good morning team,

Looking for a quick refresher on transformer selection and how it correlates to fault current contribution to a grid. Is there a major benefit in selecting a delta-delta or delta-wye or wye-delta or wye-wye when trying to limit the fault contribution. Im seeing more requirements for wye-wye nowadays as opposed to delta-wye when coming from a secondary feed and im seeing delta-delta when coming from primary and just wanted to make sure im understanding the benefits as well as tradeoffs.

“If my critics seen me walk on water they would say its because i cant swim”

- M.T.-

 

[mparenteau]

Z spec?

 

[bacon4life]

Check out the Whys of the Wyes whitepaper from ABB.

 

[Energyfit24381]

Thanks so much @bacon this is a great paper!

“If my critics seen me walk on water they would say its because i cant swim”

- M.T.-

 

[waross]

A grounded wye/delta will backfeed into a ground fault by an amount related to the impedance of the wye/delta transformer(s)

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Ohm's law
Not just a good idea;
It's the LAW!

 

[prc]

It all started with a delta-delta connection in the beginning. Then engineers found out the benefits of star connection. Benefits of delta-star connection for step-up transformers delta(LV) (HV)-star connection for distribution end with all interconnecting transformers with the star-star connection. Please see IEEE standards C57.105 and C57.12.70 and IEC 600768-8 regarding the application of connections.

 

[RRaghunath]

Star-Delta transformer with Earthed Neutral on Star and the star connected to grid, helps reduce the zero sequence impedance of the grid and hence improve fault levels during earth faults in the grid.
Delta-Star is the most popular connection for step-down transformers in Industrial substations. Transmission / Distribution
companies mandate at least one of the windings to be Delta in order to ensure that the earth faults in the power system within the industry are not reflected on to the grid / distribution network.
Star-Star or Auto transformers are more popular as Interconnecting transformers within the power grid.
R Raghunath