Step-Up Transformer 480V-4160V

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Junior_EE

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Currently working on a job where utility service comes into the building at 480V. The building is very tall, so we step up to 4160V, run up the building, then step back down to 480V to distribute power locally.

Clearly the step-down transformer is going to want to be delta-wye type.

What makes the most sense for the step-up transformer, and why? On other, similar projects, we have used a delta-wye step-up transformer, but I do not understand why we would want a neutral connection.

Any light you can shed on this situation would be helpful. If it makes any difference, I am in NYC.
Thank you.
 
Most staff are familiar with Delta-Wye transformer configurations.

The step up version does not mean that you have the use for a neutral on the secondary, it just means that you get the benefits of solidly grounding the Wye on the secondary for stability (you can resistance ground also for a stable source or I don't know why anyone would anymore, but you could leave it ungrounded if you want too).

Delta windings also help limit propagation of harmonics upstream.

Step up to distribute vertically is very typical on a highrise. Smaller busway (or cablebus) than 480V. Depending on the height, consider 13.8kV.
 
This is a totally ridiculous question--

Can you really speak of "Voltage Drop" when sending power up a high-rise? :angel:
 
If you use a 4160 delta secondary it would likely be ungrounded system, a wye secondary gives you a grounded 4160 volt system.
 
infinity said:
If you use a 4160 delta secondary it would likely be ungrounded system, a wye secondary gives you a grounded 4160 volt system.
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And if it is an ungrounded delta secondary (4160V), you would need ground fault monitoring on it, not inexpensively attained at 4160V. You could go with corner grounding it I suppose, but I'm not sure of the implications of that in a high rise.
 
Jraef said:
And if it is an ungrounded delta secondary (4160V), you would need ground fault monitoring on it, not inexpensively attained at 4160V. You could go with corner grounding it I suppose, but I'm not sure of the implications of that in a high rise.
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Where is the monitoring requirement in the NEC?
 
I'm curious why the building is served with 480 when they want ot do high voltage distribution. This seems very inefficient and costly. Why not have service delivered at 13.8?
Is this a NYC thing?
 
texie said:
I'm curious why the building is served with 480 when they want ot do high voltage distribution. This seems very inefficient and costly. Why not have service delivered at 13.8?
Is this a NYC thing?
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In NYC, and in many areas, you get the voltage that is available in that area. In many areas, there are no overhead lines so everything is underground, so he is llikely getting 480V from several transformers in parallel under the sidewalk fed from 5kV in the street. That is the standard secondary for certain capacities for Con Ed.

I did a highrise in NYC and was only given access to 208V. They had a stiff 208V grid in the street with lots of capacity, and that is what I was offered, or nothing. So we do with what we get.
 
ron said:
I did a highrise in NYC and was only given access to 208V. They had a stiff 208V grid in the street with lots of capacity, and that is what I was offered, or nothing. So we do with what we get.
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Same here, on our current project we have 4-4000 amp, 208Y/120 volt services with about ten 208 to 4160 step up transformers and another ten 208 to 480 transformers. IMO it's a lousy design as opposed to just installing 480Y/277 volt services.
 
So Consolidated Edison is distributing about the same voltages that Thomas Edison did in NYC 130 years ago, only AC instead of DC :)
 
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