Delta vs Wye primary
Delta vs Wye primary
(OP)
Several 115kv to 33kv step down transformers are scheduled for replacement, we have the option of either going wye grounded or delta for the primary. What are the pros and cons of each option? The units are between 15 and 60MVA.






RE: Delta vs Wye primary
RE: Delta vs Wye primary
Thus far I have decided to add a delta winding either in the primary or secondary of the unit to prevent zero sequence currents passing through. Currently most of the units are wye grounded-wye grounded which presents a relaying challenge since a fault involving ground also gets 'seen' in the transmission network.
RE: Delta vs Wye primary
In many cases that may be a much more significant consideration than the possible benefits of a new configuration.
RE: Delta vs Wye primary
The major driver behind having a delta connection in the transformer is to eliminate zero sequence elements from passing and to allow for harmonic/transient circulation.
However, the big question is having it either on the primary or secondary.
RE: Delta vs Wye primary
RE: Delta vs Wye primary
Just to ask:
Can a delta primary power transformer be energized without load?
RE: Delta vs Wye primary
RE: Delta vs Wye primary
RE: Delta vs Wye primary
http://www.powerqualityworld.com
RE: Delta vs Wye primary
RE: Delta vs Wye primary
RE: Delta vs Wye primary
http://www.powerqualityworld.com
RE: Delta vs Wye primary
Just one quick question. Is a delta delta connection even possible with a 115 to 33kv transformer? Just wondering.
RE: Delta vs Wye primary
http://www.powerqualityworld.com
RE: Delta vs Wye primary
RE: Delta vs Wye primary
RE: Delta vs Wye primary
What are the reason in India for primary wye?
RE: Delta vs Wye primary
NER on 33 kV seems a good solution to limit the fault current on 33 kV side and the GPR as well.
RE: Delta vs Wye primary
RE: Delta vs Wye primary
RE: Delta vs Wye primary
While a wye primary does have insulation economy, my concern is that it acts as a 'grounding transfomer' in that the delta secondary will try to 'balance' out differences. however, in theory, if all the primaries are wye on the 115kv system, wouldn't the issue be less so?
RE: Delta vs Wye primary
RE: Delta vs Wye primary
RE: Delta vs Wye primary
We (a utility) use star-star (both neutrals earthed) with a delta tertiary in instances where there is some risk of backfeed, so as not to have an unearthed system if the high-side opens up for some reason. Typical examples might be a mine with it's own generation that is capable of synchronising onto our system. In cases where there is no risk, we use a delta-star transformer with neutral earthed.
RE: Delta vs Wye primary
If the primary is solidly earthed and the secondary is NER earthed, shouldn't be a problem.
you lose the economy virtue if the utility requires a fully insulated wye, this is usually required where non-effectively earthed systems are present as the neutral voltage can jump ( very true with NER on HV side)
The delta smaller current will have a smaller winding CSA by then, but you need to have another remote end with a neutral point so you can get good ground fault protection.