Utility Owned vs Customer Owned Transformers Pros vs Cons

[philly]

As far as I know with new 480V Service entrance the utility transformer can either be customer or utility owned. Most of the time for 480V services I see the transformers as utility owned but in a few cases I have seen ones that have been customer owned.

Is there a determining factor for deciding whether a transformer will be utility owned or customer owned for a given service entrance?

If the transformer is utility owned then the metering point will be on the secondary of the transformer (metering cabinet or customer Switchgear) and the service entrance would be considered on the transformer secondary. If the transformer is customer owned then I'm guessing that the metering point will be on the primary and the service entrance will be considered the primary of the transformer. Is this correct?

What about from a primary breaker/switch perspective for isolating the 480V secondary equipment. If the transformer is utility owned with the metering on the secondary I don't believe there is anywhere on the primary that the customer can install a switch breaker be able to isolate secondary when needed and therefore will require the utility to open their switch for any sort of outage. With customer owned transformers I'm assuming there is more flexibility to install a primary switch to give the customer the opportunity to isolate system for outages when needed?

 

[iwire]

In my opinion let the utility own it.

They will handle replacement, the running costs etc.

On the other hand if the customer owns it the customer will also have to provide and handle the upkeep of a MV service disconnect and OCP.

I see no benefit at all unless the customer has other uses for MV

 

[mayanees]

Utility- or customer-owned service transformer

Utility- or customer-owned service transformer

My experience is that it's a rate determination that would drive your selection. If the Utility provider allows it for a given size of service, the rate will obviously be higher when they provide the transformer. So then it becomes an economic evaluation.

 

[texie]

As far as I know with new 480V Service entrance the utility transformer can either be customer or utility owned. Most of the time for 480V services I see the transformers as utility owned but in a few cases I have seen ones that have been customer owned.

Is there a determining factor for deciding whether a transformer will be utility owned or customer owned for a given service entrance?

If the transformer is utility owned then the metering point will be on the secondary of the transformer (metering cabinet or customer Switchgear) and the service entrance would be considered on the transformer secondary. If the transformer is customer owned then I'm guessing that the metering point will be on the primary and the service entrance will be considered the primary of the transformer. Is this correct?

What about from a primary breaker/switch perspective for isolating the 480V secondary equipment. If the transformer is utility owned with the metering on the secondary I don't believe there is anywhere on the primary that the customer can install a switch breaker be able to isolate secondary when needed and therefore will require the utility to open their switch for any sort of outage. With customer owned transformers I'm assuming there is more flexibility to install a primary switch to give the customer the opportunity to isolate system for outages when needed?

I think you have it right.
But consider where you would likely see a customer buy power at the primary level from the POCO. This would not be the average bear with a, say, a 480 volt/400 amp service to single facility. It would likely be a very large power user in a large facility or sometimes done in a campus environment where the customer takes power delivery at a primary level with a single meter and the does their own distribution within the campus.
A typical POCO will have certain minimum demand requirements before they would agree to providing primary service. Conversely, they will will will have certain maximum load demand requirements where they will force the customer to take power at the primary level.

 

[augie47]

It gets a bit confusing in this local area. The key here seems to be what the utility and customer agree on as the SERVICE POINT (NEC Term) as,locally, sometimes transformer & conductor ownership, leasing, and maintenance often varies depending on the contract.
It gets a bit confusing as a Service Point ahead of the transformer would indicate the transformer was a SDS and subject to the NEC with Art 250.30 & 240.21(C) applicable and the those requirements have changed a bit depending on the Code cycle.

 

[electrofelon]

In addition to what others have said, a few other comments. First, note that some utilities will charge the customer for the transformer (around here especially commercial customers that are upgrading existing). This doesnt mean that the customer owns the transformer, even though they paid for it. Note that for a transformer to be customer owned, there must be a service disconnect ahead of the primary. Also, note that a utility can and often will size the transformer smaller than the NEC would require, so a customer owned transformer would often be larger and more costly than what the utility can use so there is a benefit to paying them to do it under their rules. Finally, with the meter on the primary side, the customer is paying for the transformer losses.

 

[Carultch]

Also, note that a utility can and often will size the transformer smaller than the NEC would require, so a customer owned transformer would often be larger and more costly than what the utility can use.

How and why does a utility do that?


Do they have some kind of risk assessment, that shows it is more economical to let one wear out faster and replace it, than to buy a properly sized one in the first place?

 

[iwire]

How and why does a utility do that?

The NEC does not apply to them and they know NEC service calcultions are almost double the real connected load.

2,000 amp NEC service will likely never pull more than 1,000 amps

Do they have some kind of risk assessment, that shows it is more economical to let one wear out faster and replace it, than to buy a properly sized one in the first place?

It is properly sized from their standpoint.

They have years and years of historical data showing what an occupancy will really need

They also take advantage of the large thermal mass of a transfomer and will allow it to run over its rating during peak times.

Be happy they do this or all our electrical rates would be higher.

We have one customer who chooses to get their service at MV and their pad mount is bigger than I have ever seen outside of substations and industrial plants.

 

[philly]

In my opinion let the utility own it.

They will handle replacement, the running costs etc.

On the other hand if the customer owns it the customer will also have to provide and handle the upkeep of a MV service disconnect and OCP.

I see no benefit at all unless the customer has other uses for MV

What about the issue of being able to have a primary switch that the customer can open without having to rely on the utility?

What about for Arc Flash mitigation on the Service Entrance Switchgear/Switchboard? Most likely it will be extremely high at the service entrance equipment on the secondary of the transformer. If utility owns transformer there is nothing that can be done on primary. If customer owns transformer then there are several solutions on the market that can be installed on the primary in order to mitigate Arc Flash at the Switchboard/Switchgear on the secondary of the transformer.

I've seen some large facilities that have a main MV metering point on their property and then have Ariel lines with several service drops to various unit substations. In this case its all behind the utility's main meter so I guess the customer is free to do what they please. In these cases from a primary switch perspective would you just have cutouts on a pole as the primary disconnecting means or would you spend the money on a primary switch on the ground that could potentially mitigate Arc Flash?

 

[iwire]

What about the issue of being able to have a primary switch that the customer can open without having to rely on the utility?

If that is important to the customer it is worth considering but in this area it's easy to call for a disconnect.

What about for Arc Flash mitigation on the Service Entrance Switchgear/Switchboard? Most likely it will be extremely high at the service entrance equipment on the secondary of the transformer. If utility owns transformer there is nothing that can be done on primary. If customer owns transformer then there are several solutions on the market that can be installed on the primary in order to mitigate Arc Flash at the Switchboard/Switchgear on the secondary of the transformer.

I've seen some large facilities that have a main MV metering point on their property and then have Ariel lines with several service drops to various unit substations. In this case its all behind the utility's main meter so I guess the customer is free to do what they please. In these cases from a primary switch perspective would you just have cutouts on a pole as the primary disconnecting means or would you spend the money on a primary switch on the ground that could potentially mitigate Arc Flash?

That is above my pay grade,I can't provide any input on that.

But as soon as the customer has MV electrical the costs and choices of people to service it increase substantially.

What kind of facility are we talking about?

 

[steve66]

If the customer owns the transformer, the utility will always meter on the primary side, and the customer pays for the transformer losses. Not that that's a big deal - paying for the transformer losses is probably cheaper than paying for a lower delivery voltage.

At least, that's the only way I've ever seen it.

At the very least the transformer is normally provided with an internal primary disconnect, that basically disconnects power to the secondary so someone can work on the secondary without the utility having to disconnect the service.

From what I've typically seen, customers with a single service usually have a utility transformer, and customers with multiple services usually own their own transformers.

 

[mbrooke]

I agree with everything said thus far. It will not be in your benefit to own that transformer unless you have a compelling need.

 

[philly]

Note that for a transformer to be customer owned, there must be a service disconnect ahead of the primary.

Are there any requirements where this service disconnect must be located on the primary? I'm assuming it would have to be between the transformer primary and utility metering cabinet? I'm also assuming this service disconnect must have an OCPD either a fused switch or MV breaker?

At the very least the transformer is normally provided with an internal primary disconnect, that basically disconnects power to the secondary so someone can work on the secondary without the utility having to disconnect the service..

Even if the transformer is utility owned are these internal primary disconnects usually available to the customer to operate?

From what I've typically seen, customers with a single service usually have a utility transformer, and customers with multiple services usually own their own transformers.

This is usually what I see as well. Large industrial commercial/industrial complex that has a utility service entrance at the distribution voltage and then overhead lines that drop down into various service entrances. Are these really considered service entrances anymore if all these service entrances are behind the main utility meter where the overhead lines come onto the property? I have seen cases where the utility lines come onto the property, hit a utility meter and then travel overhead on property to various riser poles where there are gang operated switches, and fused cut-outs before it drops down to a transformer. What is considered the "service entrance" in this case?

 

[Tony S]

OK a question, how would an installation with multiple transformers be handled? Does the PoCo give a bulk MV supply leaving the customer to sort out the MV switching or do they maintain each individual transformer?

I’ve worked on both of the above, I know which I prefer.

 

[GoldDigger]

To some extent it would depend on what the customer ordered.
If the demarcation between utility and customer is on the MV side, they would expect the customer to provide all of the switchgear.
If the demarcation is on the Lv side, the utility would be providing multiple services (possibly with the metering at MV) and would supply all of the switchgear.
A given utility may be willing to go either way.

mobile

 

[electrofelon]

Are there any requirements where this service disconnect must be located on the primary? I'm assuming it would have to be between the transformer primary and utility metering cabinet?

Yes. Basically look at 230.82. A transformer is not on the list of items permitted on the supply side of the service disconnecting means. For a transformer to be ahead of the service disconnect, there needs to be a service point between the tranny and the disco, which makes it a utility transformer.

I'm also assuming this service disconnect must have an OCPD either a fused switch or MV breaker?

Yes in addition to the service disconnect, we also need an OCPD. 230.90.

Even if the transformer is utility owned are these internal primary disconnects usually available to the customer to operate?

Generally no. These are locked in the MV compartment. I have heard of electricians using a hot stick to pull the cutouts on the pole when needed. Recently some members on here stated they keep a hot stick and use it if necessary.

 

[electrofelon]

A minor correction/addition to what I said: Note that if we are talking about primary services, part VIII of 230 would apply, which has some specifics about disconnecting means and over-current protection, although there is nothing fundamentally different.

 

[philly]

Yes. Basically look at 230.82. A transformer is not on the list of items permitted on the supply side of the service disconnecting means. For a transformer to be ahead of the service disconnect, there needs to be a service point between the tranny and the disco, which makes it a utility transformer.

For a customer owned transformer and primary service what about a transformer that has an internal switch/OCPD? A cooper outdoor transformer has an internal VFI switch that is internal to the transformer with integral protection. Would this count as the service disconnect in this case? Or does the primary service disconnect have to be a visible, operatable, lockable, etc.... disconnect which would require a physical external switch on the primary?

Do MV switches, and breakers have UL service entrance ratings similar to LV Swbds, and Panels?

 

[electrofelon]

For a customer owned transformer and primary service what about a transformer that has an internal switch/OCPD? A cooper outdoor transformer has an internal VFI switch that is internal to the transformer with integral protection. Would this count as the service disconnect in this case? Or does the primary service disconnect have to be a visible, operatable, lockable, etc.... disconnect which would require a physical external switch on the primary?

I dont think that would fly. I think you would have multiple issues with definitions of various things. Also I am not sure if these transformer integral disconnects are rated for load breaking? Maybe others will have some comments here.

Do MV switches, and breakers have UL service entrance ratings similar to LV Swbds, and Panels?

I am not real familiar with MV gear, so again maybe someone more knowledgable in this area will chime in.

 

[truck41trouble]

Most distribution gear does have ul ratings. The poco I work for requires any mv equipment located less than 14' from a structure be listed. Its cheaper to stock one type so I think that's all we have now. Most internal transformer disconnects and gang switches are rated for load breaking.

In my area, anyone can apply for primary metering including single phase applications. The monthly delivery charge alone would equal the average persons electric bill for 3-4 months.

Our primary metering installs consist of cutouts, gang switch, pt/ct rack , customer operaple gang switch, then customer load.

Most of the time , primary metering is used when a non standard trans. Bank and non standard voltages want to be used such as 575 or 600v.

Total end load is calculated by the engineers and the building rep, then a primary service is built accordingly. Any customer using over 13mw usually opts for cogeneration, since they are required to participate in a peak load shedding programs, or rolling blackout schedule.

Oddly enough, we don't own anything after the meter, but we always set the customer poles. ?


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