Another Weird Questions - Utility Transformers and Fat Ladies in High Heels

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dema

Senior Member
Location
Indiana
I never know whether to ask the question dumb or ask the question smart. What I want is the benefit of experience.

I am an electrical engineer that gets weird jobs. Maybe all of you get weird jobs - I don't know. I've been doing this for a couple of decades now and it still seems that something I've never seen before lands on my plate once or twice a month. We do a lot of renovation design - but really? Something new that often?

There is a 70,000 sq ft building with two sets of the old single phase oil filled transformers on the roof providing three phase service. The kind with the bare stabs. One set feeds a three phase delta service of 2000A. The other feeds a three phase wye service of 800A. An investor bought the property without realizing that they would own the transformers and that the transformers would not be appropriate for converting the whole building into small offices and small apartments.

The building is downtown and is surrounded by buildings and streets. It has a narrow alley that goes to its own little courtyard. The courtyard is about 30'x35' at ground level, but half of it is covered by upper stories. There is a basement. The local utility will not put transformers on the roof. The roof will not hold 7 tons of transformer (two large padmounts) and it is doubtful it could be reinforced to do so.

There is a basement. We are looking to excavate the alley to provide entrance to the basement and do a renovation to meet the vault requirements in NEC 450.

I am looking for wisdom - something clever we haven't thought about. Words of wisdom in getting rid of the existing installation, in putting in the new, in thinking of something we haven't thought of yet. I'm thinking that this is a huge amount of money for an investor who was hoping to just reuse the existing service and make no infrastructure changes.

A structural engineer said, "Those weigh hundreds of pounds, right?" Right. And electrical fairies sit behind the outlets to provide the power. The local utility supports the magical creatures union.

Thank you.
 

JFletcher

Senior Member
Location
Williamsburg, VA
How do 2 transformers make a 3 phase wye service? :huh:

What service does the client need? Are there even 3 phases available from the POCO? If so, why not reconfigure 3 of the 4 (eta: 6 of the 6?) xfmrs to provide the (probably needed) large amperage wye service? Yes, this would involve all new switchgear, but the existing xfmrs could stay, unless he needs 2500+ amps, yes?

Istm that size switchgear would cost more than the xfmrs. and really, it is not your problem the investor bought this property not knowing all the details, unless you are the investor.

eta: 2 sets of 2 xfmrs or 2 sets of 3?
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
How do 2 transformers make a 3 phase wye service? :huh:

What service does the client need? Are there even 3 phases available from the POCO? If so, why not reconfigure 3 of the 4 (eta: 6 of the 6?) xfmrs to provide the (probably needed) large amperage wye service? Yes, this would involve all new switchgear, but the existing xfmrs could stay, unless he needs 2500+ amps, yes?

Istm that size switchgear would cost more than the xfmrs. and really, it is not your problem the investor bought this property not knowing all the details, unless you are the investor.

eta: 2 sets of 2 xfmrs or 2 sets of 3?

I will assume the OP means 2 sets of 3 single phase transformers like these.
904ewBTBfig3.jpg 904ewBTBfig1.jpg
 

dema

Senior Member
Location
Indiana
Transformers

Transformers

Yes, the little pictures are exactly right. You even laid them out like they are on the roof. One set connected in wye for an 800A service and the other in delta.

I had a niggle - and my father answered the niggle. I'm sure you've had them. The niggle turned out to be "What about PCB's?"

Sometimes I post a question not knowing what the real question is - just knowing there is one.

I am now niggle free but would appreciate any other input you have.

I was wondering about reconfiguring - asked a vendor the life span of transformers. I think these are beyond their predicted useful life - though they are still performing. He said design life of 25 years with additional life if under utilized. Well, I think these are probably some indefinite age over 50. Thank you both. (If we weren't having to rewire much of the building that would be an option still I think. But I think there would be too much work lost when a transformer blew - and what if it is PCB?)
 

dema

Senior Member
Location
Indiana
What are they called?

What are they called?

What do you call the old martian transformers? (With stabs that look like Uncle Martin's antennae if you are old enough.) "Old single phase oil filled transformers"? Is there another name? I need to research PCB's.
 
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