AC\DC
Senior Member
- Location
- Florence,Oregon,Lane
- Occupation
- EC
Ya but how long is the question
If 1/2 mile, 20 amp requires 500 kcmil, why do utility poles of many miles have such small wires?
- Thread starter Stevenfyeager
- Start date
A 225 kVA transformer burns off somewhere around 1500 watts of heat just sitting still. So over $1000 per year at my local kWh rates.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
I think your number is a little high. The Conventional rule of thumb is half a percent of KVA which would be 1100 watts. DOE 2016 units can be a lot lower. I have some 25 KVA pole units (DOE2016) that are only 48 watts no load which is about .2 percent. If I remember correctly, the DOE standards don't directly address no load losses, they just address overall efficiency. The way it is calculated typically the easiest way for the manufacturers to meet this is to lower the no load losses.
But still, I am not a fan of transformer losses for sure. Another thing to consider is if that heat is utilized or will require cooling. That can make it better or worse
pipe_bender
Senior Member
- Location
- Boston
- Occupation
- Electrician
A medium sized metal fab operation is moving to a new building my boss bid on it, but the company engineer changed from 480 to 240 delta at a meeting yesterday when the POCO said they could do a 240 delta padmount.
when we asked why they had four reasons mainly Insurance and safety program cost to have employees around over 480V.
Also they need 240v delta either way for some equipment and the cost of transformer losses are forever.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
Do you mean a 240V high leg Delta?
Birken Vogt
Senior Member
- Location
- Grass Valley, Ca
I like 240 high leg center tapped delta for small to medium occupancies like this.
Full 240 for 3 phase and 1 phase equipment, and also 120 for the office and stuff.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
I was actually asking @pipe_bender about the 240V Delta. I was wondering if it was 3Ø and had a high leg. I was asking because I have never seen a padmount transformer for 240V Delta w/high leg. It would have to have at least two transformers to accomplish this. Not many POCOs even provide an open, or closed, Delta service anymore.
Birken Vogt
Senior Member
- Location
- Grass Valley, Ca
I actually saw one last year. It was in a rural area of California served by PG&E and burned in a massive fire. Serving a tiny water treatment plant.
It would surely have been open delta on a pole before the fire. After the fire they did not put up any poles when they rebuilt the system. They ran underground to everything. I was surprised too when I saw a padmount and a center tapped delta service. So I went and looked at the tx and sure enough, that is what it was. All this to say, they do exist.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
The other consideration if in an area where you utilize heating more than cooling is these losses do lessen demand from your heating equipment. So the pros and cons can vary depending on location and application.
That’s sub transmission voltage- 35kV system. We have a circuit of that we work on.
Correct. It can be accomplished with two pad mount transformers.
The problem is when one of the two phases blows a fuse, the energized line back feeds the “dead” primary, creating either a second blown fuse or an energized “dead” line.
Hard to troubleshoot and not safe
I used to build them with CP&L as a contractor many years ago.
We have none on our system now.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I agree, that's all you ever see that used for around here, other than maybe an occasional larger industrial customer with that kind of voltage as their main service voltage.
A local POCO had a mile or so run of underground because of proximity to an airport. They one time had a fault in it and needed to repair it. Not sure why but their repair failed upon energizing, found it's way onto barbed wire fencing as well as telephone cabling in the vicinity of the repair. there were damages to phone equipment and small fires here and there originating near fencing or phone equipment within a couple miles or so all around that repair location. Might not been their repair that failed, I know they eventually replaced that entire run not too much later on after this incident.
That reminded me of this story-
About 20-25 years ago we had a section of UG cable out. We had a “Thumper”. It was a huge beast with a generator in a pull behind trailer.
Now these Thumpers come in suitcase size..
Anyway.
We had the thumper in the cable, and couldn’t get it to thump. What we do is put a high DC charge on the cable and when it jumps to the concentric neutral in the ground the arcing makes a thumping sound you can hear from 20-40 feet away.
We tried and even went to about 20kV
I thought maybe the cable wasn’t bad after all. So we put the elbow back on.
Side bar- the phone and power ran in the same ditch. There was a pedestal beside the vault.
Once we put the cable back on it immediately blew out and fire/smoke shot out of the phone pedestal.
The cable thumped fine after that.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Eh, whatevs, no one is using that phone stuff anymore anyway , except for maybe that 100 year old lady who has had it since 1952
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
NYSEG here in upstate NY has a few 35kV distro lines here and there. Based on my conversations with the planners and linemen, it seems like nobody likes them. I almost got to do an underground primary off one near Chatham. All I would have had to do is procure and pull the cable, POCO terminates each end. Still though, would have been some good bragging rights to say "I pulled some 35kv cable today". Usually when I do these it's off a 4800 Delta system so we have to pull 2 cables.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I once had to do a controls project at the Celilo Converter Station in Oregon, where they take a lot of the hydro power from the Columbia River and send it down the Pacific DC Intertie to Southern California. That Pacific Intertie is 500kVDC on two wires (so +500kV on one, -500kV on the other), meaning it is 1 million volts DC between them. When I asked why it was so high, I was told that even if you have only 1 ohm of resistance per foot of wire, to go 846 miles, there would be a lot of I^R losses. But if the current is only 1 Amp, 1^2 is still 1 and the losses are minimized. So by using 1 million V, 1 A = 1MW of power.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Yeah if you had wire that was 1 ohm per foot, you'd probably need to get up into the billions of volts to accomplish anything
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Does that mean somewhere there is a mid point tap that is likely at ground potential?
Otherwise a two wire source just has one voltage potential between the two points and with DC one is positive and the other is negative.
More on the pacific intertie here, its got quite a grounding system, thats cool @Jraef worked on it I thought part of it was SWER but that may have changed.
en.wikipedia.org