Whats your threshold for > 480V service?

[tortuga]

When designing a large electrical system from the ground up whats your MW threshold for going above a 480V service ?
Say the utility would oblige your customer and provide whatever you want and the incoming primary voltage is 12.5kV three phase and no space constraints.
1MW
2.5MW
5MW
10MW

 

[petersonra]

Most places this is driven by what the poco is willing to do. I don't think you get much in the way of choice.

1 MW at 480 is only 1200 Amps. Does not seem to me to be a lot of benefit at that level. Unless you are having to run it a long way.

 

[JoeStillman]

For large apartment buildings, we often get both services. The dwelling units are on the 208V service(s) and the house is 480V 3Ø.

That 1200A service looks appealing compared to the 3000A version at 208V, but a lot depends on what kind of building it is. If its a building with a lot of people in it, you're probably going to have a lot of 120V load. To feed that at 480V means you'll need a bunch of little transformers (if distances are long) or one big step-down.

If it's a factory or warehouse, you'll have long branch circuits or lots of 3Ø motors and 480 looks pretty good.

It's hard to sum it up in a rule of thumb.

 

[kwired]

For large apartment buildings, we often get both services. The dwelling units are on the 208V service(s) and the house is 480V 3Ø.

That 1200A service looks appealing compared to the 3000A version at 208V, but a lot depends on what kind of building it is. If its a building with a lot of people in it, you're probably going to have a lot of 120V load. To feed that at 480V means you'll need a bunch of little transformers (if distances are long) or one big step-down.

If it's a factory or warehouse, you'll have long branch circuits or lots of 3Ø motors and 480 looks pretty good.

It's hard to sum it up in a rule of thumb.

The question was when do you get medium voltage for a service voltage?

 

[JoeStillman]

The question was when do you get medium voltage for a service voltage?

Only when the utility forces me to. That MV gear is expen$ive.

 

[kwired]

Only when the utility forces me to. That MV gear is expen$ive.

If you actually have MV loads to supply how does it compare to supplying similar loads but designed for low voltage? Keeping in mind all the extra copper that would be needed for same load at 480 volts as well.

Campus type facilities also may be where it still makes sense to at least have some medium voltage for site distribution, particularly if POCO won't distribute throughout the facility, but if they do they probably will have separate billing accounts throughout the campus as well and in long run might still be best to own your own distribution?

 

[JoeStillman]

Campus distribution depends a lot on the metering like you say. If you want one meter, but feed to several buildings over long distances, you're in MV territory. If each building has it's own meter and billing account, the utility may be compelled by the tariff to invest in the primary distribution and transformers. There will be charges for all the utility work on private property.

I think there are a lot more criteria than MW of load.

 

[tortuga]

Only when the utility forces me to. That MV gear is expen$ive.

In your experience is there a number of MW where the benefits of smaller wire / gear outweighs the cost of medium voltage?
There has to be a crossover point somewhere.
If say you have a 4 MW building? That would be ~11,200A @ 208, or ~5,000A @ 480.

 

[Hv&Lv]

2.5 MW at 480 is as high as we offer. It gets too expensive to keep spares sitting around for years. We have one spare

 

[Hv&Lv]

In your experience is there a number of MW where the benefits of smaller wire / gear outweighs the cost of medium voltage?
There has to be a crossover point somewhere.
If say you have a 4 MW building? That would be ~11,200A @ 208, or ~5,000A @ 480.

Our largest load on our system was 7MW pre-bubble burst.. 480 and 208
We split it up with 2) 2.5MW 480 transformers, and 2) 1.5 MW 208s

Each XF fed to a separate MDP

 

[tortuga]

2.5 MW at 480 is as high as we offer. It gets too expensive to keep spares sitting around for years. We have one spare

Then its just primary service/metering at whatever your primary voltage is? Or do you offer a in-between voltage like 4160 or 2400?

 

[Hv&Lv]

Then its just primary service/metering at whatever your primary voltage is? Or do you offer a in-between voltage like 4160 or 2400?

7.2kV or 14.4kV depending on location

 

[kwired]

Then its just primary service/metering at whatever your primary voltage is? Or do you offer a in-between voltage like 4160 or 2400?

4.16/2.4kV is the distribution voltage in some small towns around here.

A few have upgraded in to 12.47/7.2 in recent years though, partly to make it easier to link to or from the rural system if needed as those towns are supplied by same POCO though part of reason they were not same voltage is the town wasn't always part of same POCO. Also less parts in inventory needed when you get everything on one distribution voltage system.

 

[electrofelon]

Only when the utility forces me to. That MV gear is expen$ive.

But seems like there are huge variables in that too. Couldn't I have a ganged cutout switch on a pole as my service disconnect? I don't imagine that is too pricey and basically the only MV gear needed.

 

[petersonra]

Our largest load on our system was 7MW pre-bubble burst.. 480 and 208
We split it up with 2) 2.5MW 480 transformers, and 2) 1.5 MW 208s

Each XF fed to a separate MDP

I am surprised somewhat that the poco was willing to supply 480 or 208 for such large services. I would have thought they would have brought the MV conductors to the facility property line and told the facility it was their problem from there.

 

[Hv&Lv]

I am surprised somewhat that the poco was willing to supply 480 or 208 for such large services. I would have thought they would have brought the MV conductors to the facility property line and told the facility it was their problem from there.

We are a cooperative, not for profit. We don’t see our customers as a number, but as a neighbor.

Sounds corny, but its true. I read on here so many issues with PoCos that would be a non issue with us.

Our "profits" are called margins and we give the customers back the unspent margins for the year.

Its an extremely rare instance we would tell a customer "its your problem now"..

 

[kwired]

We are a cooperative, not for profit. We don’t see our customers as a number, but as a neighbor.

Sounds corny, but its true. I read on here so many issues with PoCos that would be a non issue with us.

Our "profits" are called margins and we give the customers back the unspent margins for the year.

Its an extremely rare instance we would tell a customer "its your problem now"..

Sounds normal to me as all the power utilities in this state are publicly owned.

They don't directly give margins back to customers in general, but at same time they set their budgets to not end up with any extreme excess and do reinvest the excess into operating the system where investor owned utilities just fatten the wallets of investors with any excess. Some of them do have special community projects from time to time they fund with the margins.

The utility that serves my place has "operation roundup". Is totally optional but they round your billing to the next whole dollar. You can either pay your actual amount or the rounded up amount, your choice. They put those rounded up amounts in a special fund and every so often pick some project in the communities they serve to spend it on. Is usually something that benefits many people in the community and not just an individual or a single business.