Utility Sizing?

[olc]

Is there a set or reference criteria that utilities use to size service transformers? Or do they use their own in-house experience?

For example multi-family - if we calculate a load of say 600KVA and give that information to the utility will probably put in a 300KVA transformer. Maybe 500KVA.

 

[jumper]

Utilities follow a code called NESC. I can only guess that either it or in house experience/ engineering is used. The NEC has no say.

 

[jeremy.zinkofsky]

Utilities are they're own AHJ's so they can technically do whatever they want. However, the in house engineers reference numerous Codes, Standards, Guidelines, Historical Data, etc. to influence they're decisions. So there is no single code book that they consider exclusively.

 

[mwm1752]

Utilities are they're own AHJ's so they can technically do whatever they want. However, the in house engineers reference numerous Codes, Standards, Guidelines, Historical Data, etc. to influence they're decisions. So there is no single code book that they consider exclusively.

absolute truth -- ever see them install a 2# overhead conductor for a 200 amp service?

 

[olc]

I can show you a 176 unit multifamily with a 1700KVA calculated load on a 300KVA transformer.

 

[iwire]

Is there a set or reference criteria that utilities use to size service transformers? Or do they use their own in-house experience?

For example multi-family - if we calculate a load of say 600KVA and give that information to the utility will probably put in a 300KVA transformer. Maybe 500KVA.

They go from decades of data that lets them predict the actual load characteristics and ignore the overly conservative NEC load calculations.

This saves all of us money.



On the odd chance they goof up and undersize a transformer they are there to replace it when needed.

 

[iwire]

I can show you a 176 unit multifamily with a 1700KVA calculated load on a 300KVA transformer.

And has it failed or otherwise been a problem?

 

[Smart $]

....
This saves all of us money.
...

How so?

I only see it as saving the POCO money. You must think the POCO passes those savings on to the consumer. :happyno:

 

[iwire]

How so?

I only see it as saving the POCO money. You must think the POCO passes those savings on to the consumer. :happyno:

Hmm, yes I actually do think it saves us all money.

 

[mivey]

How so?

I only see it as saving the POCO money. You must think the POCO passes those savings on to the consumer. :happyno:

If the cost of plant goes up (bigger transformer), or if the cost of operating goes up (higher losses from bigger transformer), etc., the rates go up. Vice versa also. :happyyes:

 

[mwm1752]

How so?

I only see it as saving the POCO money. You must think the POCO passes those savings on to the consumer. :happyno:

I believe the local POCO is a based non profit regulated by the state statutes, any profits are redistributed every year back to the consumers. I get one every year. They spend whatever deemed necessary by them for operating cost. So to undersize conductors/transformers or services is per their engineered regulations. I don't believe its them being prudent in spending.

 

[norcal]

They go from decades of data that lets them predict the actual load characteristics and ignore the overly conservative NEC load calculations.

This saves all of us money.

The amount of money a utility is allowed to make is regulated, so have to agree, they will just pass the higher costs on to customer.

 

[mbrooke]

absolute truth -- ever see them install a 2# overhead conductor for a 200 amp service?

Ive see #6 AL on 200amps all the time. They know the building will never pull that power. 600kva service might get a 50kva pad if everything is gas.

 

[mbrooke]

How so?

I only see it as saving the POCO money. You must think the POCO passes those savings on to the consumer. :happyno:

When POCO spends more money it means higher bills for you and me. Larger transformers and conductors lead to increased fault current which means higher, more expensive AIC ratings. Larger transformers cost the POCO more, in addition to higher off load losses.

 

[Smart $]

If the cost of plant goes up (bigger transformer), or if the cost of operating goes up (higher losses from bigger transformer), etc., the rates go up. Vice versa also. :happyyes:

That's the thing. I'm doubtful of the vice versa part of that statement. Have you actually witnessed those costs going down, and the savings passed on to the consumer? Point in fact, I've not seen the transmission or distribution ever go down on my electric bill. I will admit that savings could be passed along in the form of no increase. Essentially, no matter which side of the fence one is on, such a claim or counter is darn near impossible to prove without being an accountant and having access to POCO books.

 

[Smart $]

The amount of money a utility is allowed to make is regulated, so have to agree, they will just pass the higher costs on to customer.

I've witnessed POCO's spend excess profits on eco-technology that they know beforehand likely does not work. I don't mind when I'm a worker on such projects, but I do realize the consumer is paying mine and my fellow workers wages.... :angel:

 

[olc]

And has it failed or otherwise been a problem?

No. I stopped by the other day just to put my hand on it t see if it seemed hot. (it wasn't)

 

[olc]

They go from decades of data that lets them predict the actual load characteristics and ignore the overly conservative NEC load calculations.

Has anyone noticed that some of the utility engineers/managers seem like they don't have the benefit of the "decades of data"?

(Basically I'm wondering if the decades of data took early retirement.)

 

[mivey]

Have you actually witnessed those costs going down, and the savings passed on to the consumer?

Yes. Both on the embedded rate side and the customer owned equipment side.

 

[mivey]

I've witnessed POCO's spend excess profits on eco-technology that they know beforehand likely does not work.

Many times the utility is forced to waste money on stupid projects by the regulating or governing authority. Just the way it is. They usually don't do that on their own because there is a good chance it would be disallowed in the rate case as a recoverable cost.