Wye-Wye

[Mike01]

Wye-Wye? Why would you use this type of transformer? I have just seen a drawing that had a substation with a primary switch and the transformer (1500/1995Kva) at 12470-480Y/277V. The drawings and specifications called for the transformer to be a ?5-leged core? for a Wye-Wye. My question is why not connect the transformer as a delta-wye is there any advantage to a wye-wye? This type will also allow currents to flow to the primary also correct?

 

[LarryFine]

Wye-Wye?

Is that a philosophical question?

Why would you use this type of transformer?

First of all, just about every modern wye service these days is wye-wye.

The only advantage I can think of is independent operation, meaning minimal load loss with the loss of a primary conductor.

There are others here much more familiar with utility systems than I am.

 

[glene77is]

Larry,
Are the phase angles maintained Wye to Wye ?

 

[LarryFine]

Larry, Are the phase angles maintained Wye to Wye ?

That's really beyond my expertise, but I believe so. A wye-wye literally is three 1ph transformers that merely share a conductor.

 

[Smart $]

That's really beyond my expertise, but I believe so. A wye-wye literally is three 1ph transformers that merely share a conductor.

I'm thinking that if a primary is truly connected wye and one leg is lost, either the winding or its feed conductor, service is maintained on the other two legs to neutral. If the primary were connected delta and one leg was lost, all three secondary phases would be affected.

 

[hardworkingstiff]

I'm thinking that if a primary is truly connected wye and one leg is lost, either the winding or its feed conductor, service is maintained on the other two legs to neutral.

OK, I understand that.

If the primary were connected delta and one leg was lost, all three secondary phases would be affected.

If one leg of the primary was lost it would affect two primary windings since each phase feeds two windings, why would the 3rd winding be affected? I don't get it.

 

[Mike01]

5-legged

5-legged

so where does the 5-legged core come in?

 

[mivey]

That's really beyond my expertise, but I believe so. A wye-wye literally is three 1ph transformers that merely share a conductor.

You believe correctly.

 

[mivey]

so where does the 5-legged core come in?

Reduces leakage flux.

 

[mivey]

My question is why not connect the transformer as a delta-wye is there any advantage to a wye-wye?

While it blocks most of the 3rd harmonics, the Delta-Wye has an issue with a loss of a primary phase in that you can get very high voltages which also cause high current unbalances; motors hate it when that happens.

This type will also allow currents to flow to the primary also correct?

3rd Harmonics will flow.

 

[glene77is]

... the Delta-Wye has an issue with a loss of a primary phase
in that you can get very high voltages
which also cause high current unbalances

Mivey,
That is an interesting idea.
Could you elaborate, just one step further,
and help me visualize this concept.

 

[jghrist]

See The Whys of the Wyes http://www.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White Papers|GET-3388B|generic

 

[Smart $]

OK, I understand that. If one leg of the primary was lost it would affect two primary windings since each phase feeds two windings, why would the 3rd winding be affected? I don't get it.

Each line powers all three windings in a delta-fed, wye-configured primary. Take away one leg of power and there is nothing to pull the floating neutral to the 120? phase angle relationship for the other two windings. The two energized windings would be series-connected line-to-line. If the primary neutral were connected, the windings would still be line-to-neutral on the loss of one leg.

 

[hardworkingstiff]

Each line powers all three windings in a delta-fed, wye-configured primary. Take away one leg of power and there is nothing to pull the floating neutral to the 120? phase angle relationship for the other two windings. The two energized windings would be series-connected line-to-line. If the primary neutral were connected, the windings would still be line-to-neutral on the loss of one leg.

OK, thanks. I misunderstood your other post. I thought you were saying a delta connected primary (on the transformer) but you were talking about a delta primary connected to the transformer in a wye configuration on the transformer primary with the neutral floating. Right?

 

[Smart $]

OK, thanks. I misunderstood your other post. I thought you were saying a delta connected primary (on the transformer) but you were talking about a delta primary connected to the transformer in a wye configuration on the transformer primary with the neutral floating. Right?

Right (if I understood you correctly ).

I generally refer to the feeder connection as "connected", and the winding-to-winding arrangement as "configured".

 

[glene77is]

See The Whys of the Wyes http://www.geindustrial.com/publibrary/checkout/GET-3388B?TNR=White Papers|GET-3388B|generic

JG,
Unreal!
Very high percentage of 3rd harmonics.