Campus Distribution System

First of all, I would like to thank you for making this incredible site, where we can ask or answer questions.

Right now, In a  third world country far, far away, where the system sub-transmission works at 60 Hz 115 KV and distribution works level is 13.8 KV,  I receive a entire uncompleted project of a "campus". Due to the project is going to be constructed by parts, for example one year a building then maybe 3 years later another and so on, I'm dealing whit which distribution design is better. A schematics goes like these: 

The buildings have an area of 500x250 mts:  Estimated Power-Demand: 1.2 MVA

I divided the building in 4 Zones and feed them with 4 pad-mounted transformers (see image, click for a larger version). 

Δ: Pad-Mounted Transformers 400 KVA in ring-bus.

---: 13.8 KV from S/E feeders.  (underground)

So my question is, in your experience is this a good distribution practice method?

Or I'm missing something? what would you believe is a critical issue here?

Or is better to put a switch-gear and then go with radial transformers? I did not mention vault transformers because the building foundations are already under construction. 

Other criteria would be to use dry-type transformers inside the building. But I don't want to get inside the building with an industrial voltage, and going inside with 480/277 V does not make sense if all air conditioners units will work at 208V according to mechanical specifications. 

I would like to thank you for taking your time to read my question. 

Distribution Planning
Underground Distribution

asked 6/19/2012
  • LuCG, a sketch may be easier for people to understand. You won’t have the privilege to edit your question yet, but if you want to upload any sketch to Tools->Document library I will add the image for you. - Steven McFadyen 6/19/2012

  • Add the image. - Steven McFadyen 6/20/2012

2 Answers

What about the top two transformers? If you isolate any one of them, all the other transformers will come under one souce.

 I would prefer two sources available for each transformer and each transformer with two switches for selecting the source (one switch for one souce). Each switch should be placed after the Toff of each source.

With ring circuit, feeder protection may be problem.



answered 6/26/2012 vkvenkataramanan 4
  • vkvenkataramanan, thank you very much for the advice, I will be updating the sketch in the next days correcting the distribution system to avoid isolation of one source if one top transformer gets isolated.

    On the other hand, what does it means "Toff"? or "after the toff of each source" (try to google or translated but no good results)

    I would like to thank you for taking your time to read my question.

    - LuCG 6/27/2012

  • vkvenkataramanan, In your experience why feeder protection may be a problem in ring circuits?

    Thank you for sharing your knowledge with us. - LuCG 6/27/2012

I don’t think you are a long way off something workable.

I may have been tempted to keep it to simple rings (rather than have cross connections). Also not sure what the HV switchgear is for – I assume you have switchgear in substation S/E.

If you don’t want 13.8 kV in the buildings then I think ring circuits with distribution transformers more or less as you have shown is better than external switchgear and radial feeds to each transformer. If inside the buildings, I may look at one 13.8 kV switch room (ring circuit) per two buildings and then radial feeds to transformers.

On the 480/227 or 208 V, you need to have these tie up. Not sure which country you are talking about, but personally I think too many voltage levels is bad. What is the normal small power single phase voltage (277 or 208). Is there any way to have only one voltage present (single and three phase).

These are just my feelings. Hopefully other people will answer and we can get some more ideas out of this.
answered 6/20/2012 Steven McFadyen 240
Steven McFadyen
  • Steven, thank you very much for the advice, you are right about the switch gear, In the next days I will update a new improved sketch.

    The Voltage Level here for distribution is:
    13.8 kV

    Low Voltage:
    480/277 V for 480 is 277 Volts. (This is more for industrial or big commercial systems )
    208/120 V for 208 is 120 Volts, so the small power single phase is 120 V.

    Is possible to have only one voltage present it will be 208/120 V directly for the transformers.
    So Transformers will be 13.8 kV - 208/120 V ( Delta-Star Connection )

    I would like to thank you for taking your time to read my question. - LuCG 6/27/2012

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