Why wye-wye?

[charlie b]

A client told me today that, in a meeting, the utility representative stated that they want the service transformers (step-down from MV to 480/277) to be configured Wye-Wye. Can you give me a good reason for this?

 

[rlundsrud]

Here is an older thread that touches on this topic.

Wye-Wye transformers

Even with a 480/277 wye power source from the poco. When needing to step down to 208/120, in my head a delta-wye transformer would still make the most sense. With not having to pull along a neutral conductor on primary side of the transformer. What are some examples and reason where a wye-wye...

forums.mikeholt.com

 

[kwired]

A client told me today that, in a meeting, the utility representative stated that they want the service transformers (step-down from MV to 480/277) to be configured Wye-Wye. Can you give me a good reason for this?

single core units or multi core units?

Around here the pole top banks made from multiple units is generally wye-wye or wye-delta.

Single core units usually have a delta primary AFAIK.

 

[electrofelon]

A client told me today that, in a meeting, the utility representative stated that they want the service transformers (step-down from MV to 480/277) to be configured Wye-Wye. Can you give me a good reason for this?

One reason is wye primaries are not subject to ferroresonance.

 

[jim dungar]

A client told me today that, in a meeting, the utility representative stated that they want the service transformers (step-down from MV to 480/277) to be configured Wye-Wye. Can you give me a good reason for this?

I would not be surprised to find that at least 75% of utility connections are Wye primaries for new installations. For sure they are more common than delta connections.

 

[Hv&Lv]

A client told me today that, in a meeting, the utility representative stated that they want the service transformers (step-down from MV to 480/277) to be configured Wye-Wye. Can you give me a good reason for this?

I just specked out three 5MVA wye-wye transformers.
These were 25 kv to 12 kV.
We can backfeed a line with them from either side of our supply

 

[dkidd]

https://library.industrialsolutions.abb.com/publibrary/checkout/GET-3388B?TNR=White%20Papers%7CGET-3388B%7CPDF&filename=GET-3388B.pdf

This goes back a ways

 

[Fred B]

Utilities around here are backing away from ungrounded delta secondaries (after substations). Statement from one lineman was a safety concern for the lineman.

 

[David Castor]

The grounded wye - grounded wye configuration is relatively immune from ferroresonance issues and is generally trouble-free for most commercial and light industrial services. It is universally used out here in the PNW by virtually all utilities that I'm aware of. Ground fault coordination is generally not a big concern. This configuration is, at least in theory, less costly since the insulation can be graded on both windings.

 

[ggunn]

Delilah?

 

[LarryFine]

Delilah?

Thank you, Tom.

 

[electrofelon]

Ungrounded wyes are actually problematic, so I think you almost always see them as grounded wye -> grounded wye. There's that famous old paper "The whys of the wyes" you can Google and pull it right up.

 

[dkidd]

Ungrounded wyes are actually problematic, so I think you almost always see them as grounded wye -> grounded wye. There's that famous old paper "The whys of the wyes" you can Google and pull it right up.

You mean the one in post #7?

 

[electrofelon]

You mean the one in post #7?

Yes. Somehow I didn't see posts #7-#8

 

[electrofelon]

Utilities around here are backing away from ungrounded delta secondaries (after substations). Statement from one lineman was a safety concern for the lineman.

What makes an ungrounded OH delta dist line less safe for line workers compared to an MGN?

 

[Fred B]

What makes an ungrounded OH delta dist line less safe for line workers compared to an MGN?

don't know, just was comment by a lineman.