830/480V Lighting circuits? 1kV rated?

[TallTimber]

Hello, I am working on a job that requires a control transformer to be installed to derive 120V from the 480V present at the Street light circuit. However after digging into it this is actually not a 277/480 circuit and is in fact a 480/830. I only plan to bring a single L-N phase to my control cabinet. It is my understanding that the primary side of my control transformer and transformer itself will need to be 1kV rated. Has anyone ever dealt with this voltage? I am reading it is only used in some street lights and oil fields. Is there any work around I am missing that will avoid me having to use 1kV equipment? At this point i think it is going to be cheaper to trench a new circuit to the cabinet.

 

[petersonra]

You can buy small pole mounted transformers for this purpose.

 

[TallTimber]

You can buy small pole mounted transformers for this purpose.

i am guessing this would have to be a custom wound transformer? pretty specific situation dropping 480/830y to 120V.

 

[electrofelon]

Wait, if you have 480 L-N aren't you fine with 600v equipment?

 

[SceneryDriver]

i am guessing this would have to be a custom wound transformer? pretty specific situation dropping 480/830y to 120V.

If the OP needs a custom transformer, I can't recommend these guys highly enough:

Custom Power Transformers for OEMs

Every GTC power transformer is custom designed & manufactured to meet your exact specifications, such as matching particular sizes, temperature ratings & more.

www.generaltransformer.com

Got me out of a pinch a few years ago with custom transformer with extremely strange requirements, and turned it around in about a week.



Sincerely,

 

[winnie]

There are several issues. The primary voltage rating of the transformer, the insulation rating relative to any voltages present, the over-all insulation rating to ground of the transformer.

A standard transformer with a 480V primary should work in this application, unless there is some sort of restriction like those of a slash rating on a breaker, meaning (say) 480V L-L, 240V L-G.

Before using a standard transformer or not, since this is an uncommon application, I'd contact a transformer manufacturer.

I wouldn't mention the 830V, since that won't be present and would confuse things. I would ask if their standard transformer is rated for 480V L-N service.

Jon

 

[petersonra]

There are several issues. The primary voltage rating of the transformer, the insulation rating relative to any voltages present, the over-all insulation rating to ground of the transformer.

A standard transformer with a 480V primary should work in this application, unless there is some sort of restriction like those of a slash rating on a breaker, meaning (say) 480V L-L, 240V L-G.

Before using a standard transformer or not, since this is an uncommon application, I'd contact a transformer manufacturer.

I wouldn't mention the 830V, since that won't be present and would confuse things. I would ask if their standard transformer is rated for 480V L-N service.

Jon

I think it is best to be upfront. There may be some none obvious issues. In any case once you tell them 480 V L-N I would hope they can figure out the rest but you never know who is answering the phone these days.

My guess is as long as you use 1000 V wire to bring in the primary voltage you are probably ok using a standard 480-120 V single phase transformer. But that is just a guess.

 

[SceneryDriver]

Hello, I am working on a job that requires a control transformer to be installed to derive 120V from the 480V present at the Street light circuit. However after digging into it this is actually not a 277/480 circuit and is in fact a 480/830. I only plan to bring a single L-N phase to my control cabinet. It is my understanding that the primary side of my control transformer and transformer itself will need to be 1kV rated. Has anyone ever dealt with this voltage? I am reading it is only used in some street lights and oil fields. Is there any work around I am missing that will avoid me having to use 1kV equipment? At this point i think it is going to be cheaper to trench a new circuit to the cabinet.

This has been bugging me: how does one get 480V L-N voltages with an 830V L-L voltage? 480V * 1.414 = 679V. 830V * 0.707 = 587V. The math doesn't track.

Am I missing something obvious, or is there a typo / math error somewhere?



SceneryDriver

 

[synchro]

This has been bugging me: how does one get 480V L-N voltages with an 830V L-L voltage? 480V * 1.414 = 679V. 830V * 0.707 = 587V. The math doesn't track.

Am I missing something obvious, or is there a typo / math error somewhere?

√3 ≈ 830/480 ≈ 480/277 ≈ 208/120, etc.

√2 ≈ 1.414 is the peak to RMS ratio of a sine wave.

 

[SceneryDriver]

√3 ≈ 830/480 ≈ 480/277 ≈ 208/120, etc.

√2 ≈ 1.414 is the peak to RMS ratio of a sine wave.

And there's the math error. It's me! Gotta stop thinking about these things and doing math in my head while I'm stuck in traffic.

Thanks.


SceneryDriver

 

[GoldDigger]

And there's the math error. It's me! Gotta stop thinking about these things and doing math in my head while I'm stuck in traffic.

Thanks.


SceneryDriver

That should be as illegal as using your cell phone while stuck in traffic!
(for some people anyway)

 

[TallTimber]

Wait, if you have 480 L-N aren't you fine with 600v equipment?

I think it is best to be upfront. There may be some none obvious issues. In any case once you tell them 480 V L-N I would hope they can figure out the rest but you never know who is answering the phone these days.

My guess is as long as you use 1000 V wire to bring in the primary voltage you are probably ok using a standard 480-120 V single phase transformer. But that is just a guess.

Wouldn't everything on the primary side of the transformer and the transformer itself have to be 1000V rated? since it is part of a 480/830 nominal system? Having a hard time wrapping my head around this as the L-N and L-L are across the typical 600V threshold.

 

[electrofelon]

Wouldn't everything on the primary side of the transformer and the transformer itself have to be 1000V rated? since it is part of a 480/830 nominal system? Having a hard time wrapping my head around this as the L-N and L-L are across the typical 600V threshold.

I dont think so, and no one has corrected me on that comment which usually happens pretty damn quickly when someone is wrong on this forum . The only thing I can think of is the article 100 definition of voltage which is:

Voltage (of a circuit). The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned.

to me, "the circuit concerned" would be the circuit from the tap/junction point and down and the greatest potential there would be 480V. There is also 300.3(C) which would require the all conductors in the wiring enclosure where the splice/tap is made to be 830 volts, so I guess you would need 1000v conductors from there to the transformer primary (or some other point outside of that enclosure). I believe XHHW is typically rated 1000V, or you could use 2kv PV wire (which is RHW-2).

 

[TallTimber]

I dont think so, and no one has corrected me on that comment which usually happens pretty damn quickly when someone is wrong on this forum . The only thing I can think of is the article 100 definition of voltage which is:

Voltage (of a circuit). The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned.

to me, "the circuit concerned" would be the circuit from the tap/junction point and down and the greatest potential there would be 480V. There is also 300.3(C) which would require the all conductors in the wiring enclosure where the splice/tap is made to be 830 volts, so I guess you would need 1000v conductors from there to the transformer primary (or some other point outside of that enclosure). I believe XHHW is typically rated 1000V, or you could use 2kv PV wire (which is RHW-2).

Extremely helpful explanation. That makes sense, This has been driving me nuts. Thank you!