Delta and Wye Systems

[electrofelon]

Thanks for the insight! I guess I am surprised by this and my gut is telling me this is a bad idea but I am having trouble coming up with any legitimate reasons. The first thing I think of is losses. The conductors themselves between the substation wye txfr and the distribution delta acting as a resistive load and enabling a circulating current. Maybe an inherent impedance mismatch between the transformers? I mean, transformers that convert from wye to delta exist all over just fine but they also have a core that acts as the interface. But here the interface is distribution lines, which I suppose in this case, is forced to act like a core?

The other thing is... why? Why connect a delta txfr to a 4-wire wye distribution system only to convert it to wye again on the secondary side? Just to avoid having to run a neutral? Work practice/safety?

I haven't even begun to think about the implications of taking a single phase lateral off this setup. But again, I'm an idiot and I am probably just creating some high school drama in my own head. I mean, these systems have been in operation for ages.

I would say for starters, I would switch it around and say why take a neutral to a primary of a transformer if it's not needed? you seem to have some false belief that a load configuration has to match its source configuration. In this case Delta or wye just refers to the configuration of the coils inside the transformer. Now that said there are quite a few intricacies of transformer configurations, but it doesn't really have anything to do with "matching" a primary to the configuration of the secondary of an upstream transformer. Actually wye wye transformers can be problematic and have some issues that need to be considered (there's an old paper called the "why's of the wyes" if you want to check it out, it's pretty hefty on electrical theory be forewarned). A Delta wye transformer has less "issues" in fact.

 

[jim dungar]

... my gut is telling me this is a bad idea but I am having trouble coming up with any legitimate reasons.

You are having a hard time because their are not any major reasons why it is bad.

Yes, each configuration has advantages and disadvantages but they need to be balanced against each other. However circulating currents is not a concern I have ever addressed when applying transformers in general industrial situations up to 34.5kV.

 

[electromagnuts]

Ho... 1967! That's one year older than my Camaro! Again, that writeup seems to be speaking about making the transition in/at the transformer as opposed to out in the middle of the system. Thanks for pointing out the paper though. I think I am concerned that a lot of these systems were thoughtfully designed a certain way many years ago and those engineers and the equipment they used are long gone. Then along come the new engineers who don't have the same fundamental knowledge, and they just hook things up up willy-nilly because they got tossed into the deep end and they are just following the standards. Combine that with all the salesmen running around spouting buzz-words and "smart" this and that everyone gets excited about. Or all these companies making grid-edge tech with venture capital then going out of business in a few years. Meanwhile it's your signature on the drawings!

 

[wwhitney]

On this question of delta supply vs wye supply, take the diagram in post 32, and suppose you are looking at/examining/metering the 3 phase conductors at a location between the two transformers. Is it even possible to tell whether the transformer supplying them has a delta secondary vs a wye secondary? Or are they electrically indistinguishable?

Cheers, Wayne

 

[electromagnuts]

In circuit theory, you can transform delta to wye and back but the impedances change. So if you thought you were impedance matching a transmission line but your source assumption is flipped, your actual impedance is maybe three times different?

 

[jim dungar]

In circuit theory, you can transform delta to wye and back but the impedances change. So if you thought you were impedance matching a transmission line but your source assumption is flipped, your actual impedance is maybe three times different?

I have never impedance matched a customer owned transformer to a utility owned distribution system, but I have only been at this for 45 years. Other than insulation to ground and protective device settings I usually never even care if the source is a wye or delta.

 

[zooby]

If videos are your thing, I've only watched a couple of this guy's, but they were pretty good. I haven't specifically watched these:

He's got some other videos on transformers as well.

Cheers, Wayne

I really like this gentleman. great instructor imo.