electrical upgrade

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raiderUM

Member
Location
Ohio
Guys,

We are doing an electrical upgrade for one of our existing buildings and this involves us moving from 4160V to 12470V primary.

The proposed design is attached. View attachment photo.pdf

We have the been metering the 208V and I have 4 years of historic data showing the 208V, which is also attached. View attachment load.pdf


Why would the engineer want to back feed the existing gear out of the new gear and have such a large transformer for the 208V? The 208V load for the entire building averages 107KW and has a peak of 303KW. A 750KVA transformer is much larger then we need.

Why would he not want to use the spare 300KVA 12.47V/208V pad mount transformer that we have from a previous job?

Based on the load profile could we not size the transformer and gear to the historic data of the building?


I am no electrical engineer.....I am just trying to understand where he is coming from
 
SPERRY-1

SPERRY-1

Member
Location
Manhattan, Kansas, United States
big picture

big picture

Could you take a bigger photograph of the diagram please? Id like to see the big picture (literally) before I try to analyze. My first guess would be backdoor spare, in case you guys decide to add equipment in the future. But I can't see all of the loads so that's only a guess.
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
I also do not know why as I don't like under loading transformers because of the losses that transformers can cost you in unused magnetizing currents, utilities will under size a transformer just because of this unless it is on your side of the cash box (meter) you will be paying for energy that you are not using, I would definitely find out and at least voice your concerns, if loads are added at a later date then a larger transformer or additional transformers can be installed, this would be like installing a 100 hp motor for a load that only requires a 25 hp motor, true transformers are not as bad as an over sized motor would be, but if your not planing to expand on more loads in the near future then it would save you more sizing the transformer closer to the loads it serves, even if you have loads that might draw a higher current for a few seconds will not cause a problem as most transformers will take quite a bit to start causing a problem as damage is a thermal problem and the mass of the windings and core can take a while to heat up so over loads of short durations in most cases are not a problem.
 
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raiderUM

Member
Location
Ohio
R

raiderUM

Member
Location
Ohio
hurk27 said:
I also do not know why as I don't like under loading transformers because of the losses that transformers can cost you in unused magnetizing currents, utilities will under size a transformer just because of this unless it is on your side of the cash box (meter) you will be paying for energy that you are not using, I would definitely find out and at least voice your concerns, if loads are added at a later date then a larger transformer or additional transformers can be installed, this would be like installing a 100 hp motor for a load that only requires a 25 hp motor, true transformers are not as bad as an over sized motor would be, but if your not planing to expand on more loads in the near future then it would save you more sizing the transformer closer to the loads it serves, even if you have loads that might draw a higher current for a few seconds will not cause a problem as most transformers will take quite a bit to start causing a problem as damage is a thermal problem and the mass of the windings and core can take a while to heat up so over loads of short durations in most cases are not a problem.
Click to expand...

I asked the electrical engineer for this project why he did not want to use the 300KVA transformer??? I mentioned that this 300KVA was surplus from another project and on this current project is a very tight budget, which would allow us to save some easy money. Also, this 300KVA transformer is a pad mount and not a dry type, so it wont be as loud.

He responded to my questions saying, I wanted to install the 750kVA transformer because anyone coming in after me would see the 3000 amp gear and wonder why I undersized the transformer so much. I also wanted to install the 750kVA transformer dry type because it would be cheaper then a pad mount, which will keep cost down.

I really wanted to ask him why we needed 3000 amp gear when the original gear is 28 years old. The 208v main gear needs replaced anyways, so why are we setting new 208v main gear to re-feed the existing 208v gear? I am guessing the sizing of the main gear is so large because of the potential of everything downstream...

Thanks
 
N

north star

Senior Member
Location
inside Area 51
: ~ :
"Why would he not want to use the spare 300KVA 12.47V/208V pad mount transformer that we have from a previous job?

Based on the load profile could we not size the transformer and gear to the historic data of the building?

I am no electrical engineer.....I am just trying to understand where he is coming from"
Click to expand...
Maybe the EE has overdesigned the project [ actual ] needs for
monetary gains...........Sometimes projects are "overdesigned"
because the overall value of the project goes up, hence, a
bigger payment to the RDP !

~ : ~
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
north star said:
: ~ :

Maybe the EE has overdesigned the project [ actual ] needs for
monetary gains...........Sometimes projects are "overdesigned"
because the overall value of the project goes up, hence, a
bigger payment to the RDP !

~ : ~
Click to expand...

and sometimes it actually costs less to buy something that "ought" to be less expensive.

it could also be that this is just a standard design and the engineering time to change it to a lower rated piece of equipment is not worth it.

or it might be that the OP is not aware of the reason and is unlikely to be told because management does not want him to know why it is being done. maybe an expansion project?
 
R

raiderUM

Member
Location
Ohio
petersonra said:
and sometimes it actually costs less to buy something that "ought" to be less expensive.

it could also be that this is just a standard design and the engineering time to change it to a lower rated piece of equipment is not worth it.

or it might be that the OP is not aware of the reason and is unlikely to be told because management does not want him to know why it is being done. maybe an expansion project?
Click to expand...

I can not see a expansion project being done here at this building. It has not been upgraded in 30 years and this building wont be touched until another 30 years.

We had a meeting yesterday with the project manager and we voiced our concern. Basically this is our only time to get the infrastructure correct and if that means we have to bring in another Electrical Engineer as a consultant, we will.
 
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