Ungrounded Wye

mivey

Senior Member
Marc,

If it helps you see it, the pole-top pins have insulators to path the long run between the outside bushings to close the delta on the primary side.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
take a second look at the primary side, you said it is delta fed, that is not correct. Delta does not have any of the three bushings paralleled. The 3 primary bushings on each can are tied together, then are bonded to ground. The secondary side is the same, but are not ground, nor have neutral wires.

The primary side would have the first and last terminal tied as phase 1, the 1st and 2nd transformer's 2 closest bushings would be tied with a jumper and fed as phase 2., and the 2nd and 3rd transformer's closes terminals would be tied together and connected to phase 3 of the incoming system. There isn't a any neutral because it was meant to be this way, to use less power. When the old timers in the industry started to fade away, so did this method, and to this day, nobody teaches this anymore. In essence, only one phase is used from the POCO to feed the facility, the last 2 phases pick up their energy by a resonance that happens within an electric motor from some strange reactive energy brought in either by induction or capacitance of some sort. Not completely understood but it happens and we still have some of this out there that hasn't been upgraded yet.
??

I see H1(A) tied to H2(C), H1(C) tied to H2(B), and H1(B) tied to H2(A). No ground... looks pretty Delta to me..
 
Ungrouded wye and delta are the same thing. The only thing different is the transformer secondary is wye and left floating rather than delta; everything else is exactly like an ungrounded delta. Very common. This allows for one transformer stock to cover both 277/480 grounded wye customers as well as 480 volt customers seeking an ungrounded system. The bond strap is simply removed from the XO bushing, rather than having to order a delta secondary unit which works the same as a wye with the strap removed.


Just to point out, where the secondary is left floating or is anything other than grounded wye, having a delta primary connection is a good idea. All else is the same.
Can I ask why it is better to have a delta primary if secondary is floating wye? What about a floating wye primary, is it the same? Thanks.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Can I ask why it is better to have a delta primary if secondary is floating wye? What about a floating wye primary, is it the same? Thanks.
Foating wye-floating wye is not a stable connection especially when dealing with 3 separate cans- none of them will magnetize at the same time and the neutral point will float away from zero.
 
Thanks for the quick response. We are purchasing transformers, but hesitate between the connection of "Grounded-wye to Floating-wye" or "Delta to Floating-wye". We know we need a floating-wye secondary, but not sure how to connect the primary.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
Thanks for the quick response. We are purchasing transformers, but hesitate between the connection of "Grounded-wye to Floating-wye" or "Delta to Floating-wye". We know we need a floating-wye secondary, but not sure how to connect the primary.

I second that... why do you need a floating wye?
 
I second that... why do you need a floating wye?
We need to replace the transformer bank that supplies a 600v customer. The current connection is delta to delta. The customer may convert to 347/600v four wire in the future. So, for now, we need to continue the 600v supply. If we buy three 347v transformers and float the neutral, we can supply that 600v. When the time comes, we can easily switch to grounded-wye.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
We need to replace the transformer bank that supplies a 600v customer. The current connection is delta to delta. The customer may convert to 347/600v four wire in the future. So, for now, we need to continue the 600v supply. If we buy three 347v transformers and float the neutral, we can supply that 600v. When the time comes, we can easily switch to grounded-wye.
If the primary is delta now, then I would go with delta primary now.

Ungrounded secondary wye will work.

BTW- what voltage are you using? I ask because ferresonance is more common above 15kv with single pole switching.
 
Top