- Location
- Illinois
- Occupation
- retired electrician
Is this a 25 kVA transformer? I think so, but since three of these are feeding a new 1200 amp service, I am not sure.
Transformer size
- Thread starter don_resqcapt19
- Start date
Deltaforce
Member
- Location
- India
- Occupation
- Electrical Engineer
25kva or 150kva?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Looking at the size relative to the pole,arrestors, etc seems pretty reasonable. I installed some 25 kava pole mounts earlier this year so kind of up on the physical size.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
FWIW, I just got demand data on a 2000 amp service and it was only 350 amps, so that sizing is certainly potentially reasonable.
Deltaforce
Member
- Location
- India
- Occupation
- Electrical Engineer
Poo
A fault at service disconnect, poco transformer ocd if any operate first
Poor coordination protective devices Operation then
A fault at service disconnect, poco transformer ocd if any operate first
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
I really have no idea what you're saying, nor do I understand .what coordination has to do with my comment.
- Location
- Illinois
- Occupation
- retired electrician
This was an upgrade from 600 amp 120/240 to 1200 amp 208Y/120 to support air conditioning that was added to a school. The secondary conductors appear to be three sets of 600 kcmil, but it sure looks like 25 kVA transformers to me.
A true 1200 amp service would require three 150 kVA transformers...not even sure you could support three 150 kVAs on a pole. I think they are around 1800 pounds each.
A true 1200 amp service would require three 150 kVA transformers...not even sure you could support three 150 kVAs on a pole. I think they are around 1800 pounds each.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Generally i think that would be ok. Did a service 4 years ago that had (3) 166 KVA. My home town has a (3) 333 bank. Not saying those poles are loving life though
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I think what @Deltaforce was saying is that the utility owned OCPD devices on the transformer would likely open before the customer owned OCPD devices in the service equipment.
This _might_ be true on overload, but AFAIK there are no requirements for selective coordination between utility and service equipment, and it is quite likely that the utility understands the actually expected load presented by the building with the 1200A service.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
IIRC, MV side fusing is often about 3x transformer FLC, at least that is whAt Eaton recommend in a paper, of course utilities might have their own guidelines and strategies.
- Location
- Illinois
- Occupation
- retired electrician
They may be looking at the actual loads on the old 600 amp 120/240 volt service, but a substantial amount of new air conditioning load was installed and they don't have any idea what that load may be.
- Location
- Illinois
- Occupation
- retired electrician
My understanding is that the typical utility transformer sizing is based on the largest fuse that they can use, but small enough to to coordinate with the next upstream distribution circuit OCPD. No intent to provide any real protection for their transformers.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Was that service upgraded without utility knowledge? Unless it was done on the DL, wouldn't the utility know about the increased load?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Hopefully the utility was involved in the change from single phase to three phase, but I know there are a few especially talented electricians out there
- Location
- Illinois
- Occupation
- retired electrician
The are pretty lax on looking at proposed new loads.
The utility installed the new transformer bank and even had to run a couple of spans of for the third phase as there were only two ungrounded conductors at the location. The third phase was added along with a pole for the three new transformers.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Oh I missed that the old service was single phase
- Location
- Illinois
- Occupation
- retired electrician
Yes, so 1200 amp three phase is a big increase in capacity compared to the old 600 amp single phase one.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Most power companies do not care about a lack of coordination with customer secondary side OCPD. They worry about the primary side coordination with the rest of their grid.
I once looked at the coordination for a major sports arena. There was no acceptable coordination with the utility. They finally agreed to closely monitor and even tweak settings on several of their relays when games were being played and broadcast.
After reminding them of the blackout at an NFL game at the Superdome.
Last edited:
fastline
Senior Member
- Location
- midwest usa
- Occupation
- Engineer
I didn't do deep scanning and searching of a picture but no way those are 150s. 25s look very consistent with the piggies vs the pole. I've seen 150 piggies and you would know. I'm just baffled with the size of that service. Even if it is a building full of electric gerbil feeders, any rational math I got does not compute. Flip the switch and my bet is the POCO will be back within a week to fix that huge whiff.
- Location
- Illinois
- Occupation
- retired electrician
I am pretty sure they are only 25s. It is possible they are still running on the 600 amp single phase service as the utility has not cut that transformer loose and it only feeds the school.