Connecting 2400/4160Y to 4160 ungrounded delta?

[hockeyadc]

Is it possible to connect a distribution transformer with a primary rating of 2400/4160Y and 2 bushings to an ungrounded 4160 delta configuration? This is coming off of the tertiary of a transformer. My understanding is that this is a 2400 phase to ground rating, and would work at 4160 phase to phase with no ground? Or is that incorrect and we actually need a 4160/7200Y transformer to connect phase to phase to this ungrounded delta?

 

[winnie]

If I understand your question, you are talking about a single phase transformer rated for 4160V L-L and 2400V L-G.

Ask yourself this: what is the L-G voltage of your ungrounded delta? Now what happens to that L-G voltage when you have a fault?

During faults, your ungrounded system could have more than L-L voltage to ground.

This is not my field, but I don't think the transformer will be suitable

Jon

 

[hockeyadc]

Well since its an ungrounded delta, the L-G voltage should be 0, meaning we have to connect phase to phase. I think I actually figured it out. I agre with you, the 2400/4160Y transformer only has coils rated for 2400 so it wont work. We need coils rated for 4160 to run phase to phase on the ungrounded delta

 

[hockeyadc]

The confusion comes in because as you said(and my understanding), its rated for 4160 L-L, so since its a 4kV open delta you have to connect L-L which would be 4160.

 

[electrofelon]

It would be helpful to see the nameplate of the transformer. But if your callout is correct, per IEEE Std C57.12.00-2015 the official designation is as follows:

A E/E1Y (such as 2400/4160Y) shall indicate a single phase transformer, with a winding of E volts that is suitable for 'connection on an E volt system, or for Y connection on an E1 volt system.

So because you have two bushings, your transformer is suitable for a grounded or ungrounded 2400 supply, the former of course would be L-N or a 2400/4160Y system. It appears this is not the right transformer for your needs.

 

[winnie]

Your error is saying that the L-G voltage would be 0.

With an ungrounded system the L-G voltage is poorly defined.

When everything is working perfectly, capacitive coupling and expected leakage will lead to almost wye voltages.

But if one phase faults to ground, that phase will have 0V to ground while the other phases will be 4160V to ground.

An ungrounded system can operate for an extended period with one phase faulted, which means you have to design with the expectation that any phase can have full L-L voltage as the L-G voltage.

Jon

 

[hockeyadc]

It would be helpful to see the nameplate of the transformer. But if your callout is correct, per IEEE Std C57.12.00-2015 the official designation is as follows:

A E/E1Y (such as 2400/4160Y) shall indicate a single phase transformer, with a winding of E volts that is suitable for 'connection on an E volt system, or for Y connection on an E1 volt system.

So because you have two bushings, your transformer is suitable for a grounded or ungrounded 2400 supply, the former of course would be L-N or a 2400/4160Y system. It appears this is not the right transformer for your needs.

My issue is that this is an ungrounded 3 wire 4160 delta system its connecting to, not a 4 wire delta. In that sense, its the same thing as an ungrounded WYE, so L-L 4160 would still work no?

 

[winnie]

And electrofelon's post makes it clear that my understanding is not quite correct.

Per his reference the transformer likely has a 2400V primary, not a 4160V primary, and is suitable for a 2400V L-N or 2400V L-L connection.

Jon

 

[electrofelon]

My issue is that this is an ungrounded 3 wire 4160 delta system its connecting to, not a 4 wire delta. In that sense, its the same thing as an ungrounded WYE, so L-L 4160 would still work no?

And electrofelon's post makes it clear that my understanding is not quite correct.

Per his reference the transformer likely has a 2400V primary, not a 4160V primary, and is suitable for a 2400V L-N or 2400V L-L connection.

Jon

a 2400/4160Y single phase transformer has a 2400V winding. I think such a unit would always be 2 bushing. If it were marked with a "GRDY" in the callout it would likely be single bushing, but still a 2400V windiong.

 

[hockeyadc]

a 2400/4160Y single phase transformer has a 2400V winding. I think such a unit would always be 2 bushing. If it were marked with a "GRDY" in the callout it would likely be single bushing, but still a 2400V windiong.

Yes its got 2 bushings. So you don't believe phase to phase 4160 will work? Since it has 2 bushing I believe phase to phase would be 4160 not 2400

 

[LarryFine]

A 1ph transformer will only have a single primary voltage rating. That's the voltage it should receive.

With two bushings, it will not care whether the source has a grounded conductor.

 

[hockeyadc]

A 1ph transformer will only have a single primary voltage rating. That's the voltage it should receive.

With two bushings, it will not care whether the source has a grounded conductor.

I see, so the coil is rated for 2400 regardless and if I connect 4160 L-L from an ungrounded delta we are going to have issues regardless of the number of bushings.

 

[LarryFine]

I see, so the coil is rated for 2400 regardless and if I connect 4160 L-L from an ungrounded delta we are going to have issues regardless of the number of bushings.

IF it's only rated for 2400v, that's correct.

 

[hockeyadc]

IF it's only rated for 2400v, that's correct.

Got it, thats what I need to confirm. I believe its only rated for 2400 based on the nameplate saying 2400/4160Y

 

[hockeyadc]

Heres the nameplate as well

 

[electrofelon]

Yes its got 2 bushings. So you don't believe phase to phase 4160 will work? Since it has 2 bushing I believe phase to phase would be 4160 not 2400

no it will not work at 4160.

 

[LarryFine]

I believe its only rated for 2400 based on the nameplate saying 2400/4160Y

You would normally see that on a 3ph unit, but there would be at least three HV bushings.

Showing 4160Y on a 1ph transformer would only be for informational purposes at best.

 

[hockeyadc]

You would normally see that on a 3ph unit, but there would be at least three HV bushings.

Showing 4160Y on a 1ph transformer would only be for informational purposes at best.

Ahhh that's where the confusion is. The assumption I had is that it's 2400 phase to ground 4160 phase to phase which is incorrect.

So another solution. If I have 2 of these with 2 bushings each, why not tie the primary side together in series and run across phase to phase on the delta? This would give me 2400 across each right?

Edit: just kidding, after typing this out I realized it wouldn't work either the voltage would half I need it to be 2400

 

[LarryFine]

In series, each primary would receive half of 4160, or 2080, along with reduced secondary output.

However, there would be instability in the secondaries because two units don't share a single core.

 

[hockeyadc]

In series, each primary would receive half of the 4160, or 2080, along with reduced secondary output.

However, there would be instability in the secondaries because two units don't share one core.

Yeah realized that as soon as I typed it lol we would need 3 units really but even then it's not ideal. I don't see anyway to make this work with 1-2 units off of an ungrounded 4160 delta