Utility 7.62/13.2 to 4800

[electrofelon]

I saw this today, mildly interesting example of utility refeeding old circuits with a newer system. Primary is fed with a hot and a neutral of a 7.62/13.2 wye system, secondary is 4800, very common in former Niagara Mohawk territory here in central NY. Note the transformer has taps for use on 2400/4160 systems also (zoom in on the third pic and you can make out the dataplate). This is near the intersection of a state road with a small town road. Apparently the state roads lines got upgraded somewhat recently but the town road still has the 4800 system. Actually what got me looking at this is the more interesting part: I saw a national grid worker taking the temp of the tranny with a IR temp gun. This was on a Saturday. do you think they are worried about this one, or is this pretty standard to send guys out to temp the transformers on weekends? Do they do residential areas on Saturdays because they figure that is when the usage will be highest with people home?

As a bonus, check out these towers. Never seen anything quite like this, they look old.

 

[mbrooke]

Neat- we have a ton of those around here for the old 4kv systems which still exist on almost every other side street.


I will let the POCO guys chime in on the IR readings. 500kva is one the large side for these step downs, I'd imagine some good load down the line.

 

[electrofelon]

Neat- we have a ton of those around here for the old 4kv systems which still exist on almost every other side street.


I will let the POCO guys chime in on the IR readings. 500kva is one the large side for these step downs, I'd imagine some good load down the line.

I can always rely on you to enjoy my posts on utility infrastructure

As far as I know, not a lot of 4160 around here - at least not in the rural areas. So 4160 originated from upgrading the original 2400 systems to 2400Y/4160. I wonder how this 4800 fits in. Was that the voltage we got from the get go - and still have- up here? Maybe we got power late enough where they had moved beyond 2400?

 

[mbrooke]

I can always rely on you to enjoy my posts on utility infrastructure

:lol: No doubt :thumbsup:

As far as I know, not a lot of 4160 around here - at least not in the rural areas. So 4160 originated from upgrading the original 2400 systems to 2400Y/4160. I wonder how this 4800 fits in. Was that the voltage we got from the get go - and still have- up here? Maybe we got power late enough where they had moved beyond 2400?

Some POCOs choose to double 2,400 either latter on or from the start. Some lines remained delta as did some 2,400 lines, while others were upgraded to multi grounded wye (4.8/8.3Y). Interestingly, 8.3/14.4 is a relatively popular voltage. This is interesting regarding the history:


http://www.cooperindustries.com/con...es/library/201_1phTransformers/TC202001EN.pdf

 

[mbrooke]

I can always rely on you to enjoy my posts on utility infrastructure

As far as I know, not a lot of 4160 around here - at least not in the rural areas. So 4160 originated from upgrading the original 2400 systems to 2400Y/4160. I wonder how this 4800 fits in. Was that the voltage we got from the get go - and still have- up here? Maybe we got power late enough where they had moved beyond 2400?

Chances are 4800 was chosen because of the rural nature- less voltage drop in that you are covering a MUCH, MUCH greater distance. Remember, 5kv for several reasons (mainly voltage drop) was fed from small, local substations. A single town might have several of these with distribution lines going no longer than a mile or two. Typical transformer size was 6.25MVA- and these were usually fed from either 12, 13.8, 23, 24.9, 27.6 or 33kv subtransmission. Sometimes higher. As a result rural POCOs had a much greater incentive to use 4.8kv when any given distribution feeder had to travel more than several miles.

This still holds true to some degree today. A POCO is more likely to choose 34.5kv when dealing with a predominantly rural area then say 13.8kv in a metro area. However as load growth increases, automatic restoration becomes more common, and that 2 120MVA transformers are cheaper than 2 50 MVA transformers (price vs MVA increase is not linear)- let alone the elimination of one or two substations resulting- the trend is to use 25kv and 35kv equipment more often where 15kv class remained predominantly supreme for 40+ years.

 

[mbrooke]

I wonder how this 4800 fits in.

View it like this: double the voltage for any given current and you can double the distance while having the same voltage drop. Halve the current for any given voltage and you can double the distance for the same VD. Now, combine the two and you can run that line 4x the distance using the same conductors. So if an 800kw 2.4kv line could travel 4 miles, you can now run that same 800kw line 16 miles. And if your rural loads are lighter than your district loads (that chance is very real), you can push 30+ miles. All in all 4,800 economically served for the distance given.

I always recommend playing around with a voltage drop calculator. Increasing the voltage, going from single phase to 3 phase, from delta to wye, ect will present a stark gain in favor of efficiency. Same fun can be had with any other parameter, ie as you increase frequency you get very small and lightweight equipment- but substantially increased losses in power transmission Xc= 1/(2piFC). There is no such think as an arbitrary number, everything is either a compromise between many or calculated precisely to meet a well defined parameter.

BTW- I once calculated the best power frequency at 72Hz.

 

[GoldDigger]

View it like this: double the voltage for any given current and you can double the distance while having the same percent voltage drop....

FIFY

 

[mbrooke]

FIFY

Technically

 

[electrofelon]

Chances are 4800 was chosen because of the rural nature- less voltage drop in that you are covering a MUCH, MUCH greater distance. Remember, 5kv for several reasons (mainly voltage drop) was fed from small, local substations. A single town might have several of these with distribution lines going no longer than a mile or two. Typical transformer size was 6.25MVA- and these were usually fed from either 12, 13.8, 23, 24.9, 27.6 or 33kv subtransmission. Sometimes higher. As a result rural POCOs had a much greater incentive to use 4.8kv when any given distribution feeder had to travel more than several miles.

This still holds true to some degree today. A POCO is more likely to choose 34.5kv when dealing with a predominantly rural area then say 13.8kv in a metro area. However as load growth increases, automatic restoration becomes more common, and that 2 120MVA transformers are cheaper than 2 50 MVA transformers (price vs MVA increase is not linear)- let alone the elimination of one or two substations resulting- the trend is to use 25kv and 35kv equipment more often where 15kv class remained predominantly supreme for 40+ years.

So 4800 was used right from the start in some places.
For some reason I thought 4800 came later due to technological and equipment limitations.

So now, if we were starting from scratch, would we be looking at lots of 35 kv class being installed? Man, we've come a long way since 2400

 

[mbrooke]

So 4800 was used right from the start in some places.
For some reason I thought 4800 came later due to technological and equipment limitations.

Indeed- I have even read 7,200 volts being used in some places from the start including the linked document. In fact, in the late 1800s 1,200 volts was actually a standard and commonly used distribution voltage in urban electrification in conjunction with 2,400. As power systems grew the 1,200 once thought to become a dominant standard, was quickly abandoned.

So now, if we were starting from scratch, would we be looking at lots of 35 kv class being installed? Man, we've come a long way since 2400

Yup- 35kv would be the dominant standard by a long shot. As would 230kv where 115 and 138kv are used today and 500kv where 345kv is used for transmission.

FWIW Manhattan and Bronx networks are 13.8kv, Brooklyn and Queens at 27.6kv, and Staten Island at 33kv. I am not 100% sure of Con Edison's history, but I think that also had something to do with when electrification picked up steam in the area. BTW Con Edison has been working in conjunction with Southwire and DHS to develop high capacity fault current limiting super conductors to be used in Manhattan due to the extreme congestion.


https://www.technologyreview.com/s/407969/a-more-robust-grid-for-manhattan/


http://www.businesswire.com/news/ho...erconductor-Cable-Consolidated-Edison-Project

Interesting technical PDF:

http://mydocs.epri.com/docs/PublicMeetingMaterials/MRNYPKPLTGV/18-MCCALL-ABOUYAALA-HYDRA_Update.pdf


The real issue however is that its not easy to move a whopping 80MVA+ of load at 13.8kv. You need 3x more cables, 3x the current on any bus section and a generous increase in fault current everywhere throughout the system requiring some serious none standard equipment. But- there was no way of knowing what the load was going to be in 1913 and they are basically stuck with it. POCOs that are dealing with "disposable" transformers (pole pigs) have it easy.

 

[electrofelon]

Indeed- I have even read 7,200 volts being used in some places from the start including the linked document. In fact, in the late 1800s 1,200 volts was actually a standard and commonly used distribution voltage in urban electrification in conjunction with 2,400. As power systems grew the 1,200 once thought to become a dominant standard, was quickly abandoned.





Yup- 35kv would be the dominant standard by a long shot. As would 230kv where 115 and 138kv are used today and 500kv where 345kv is used for transmission.

FWIW Manhattan and Bronx networks are 13.8kv, Brooklyn and Queens at 27.6kv, and Staten Island at 33kv. I am not 100% sure of Con Edison's history, but I think that also had something to do with when electrification picked up steam in the area. BTW Con Edison has been working in conjunction with Southwire and DHS to develop high capacity fault current limiting super conductors to be used in Manhattan due to the extreme congestion.


https://www.technologyreview.com/s/407969/a-more-robust-grid-for-manhattan/


http://www.businesswire.com/news/ho...erconductor-Cable-Consolidated-Edison-Project

Interesting technical PDF:

http://mydocs.epri.com/docs/PublicMeetingMaterials/MRNYPKPLTGV/18-MCCALL-ABOUYAALA-HYDRA_Update.pdf


The real issue however is that its not easy to move a whopping 80MVA+ of load at 13.8kv. You need 3x more cables, 3x the current on any bus section and a generous increase in fault current everywhere throughout the system requiring some serious none standard equipment. But- there was no way of knowing what the load was going to be in 1913 and they are basically stuck with it. POCOs that are dealing with "disposable" transformers (pole pigs) have it easy.

Cool stuff. Wow only 13.8 for Manhatten and the Bronx! :jawdrop:

 

[mbrooke]

Cool stuff. Wow only 13.8 for Manhatten and the Bronx! :jawdrop:

Yup- typically serving something like 150MW to 200MW with several 300MW+ networks. Up to 28 13.8kv cables. Here is an excerpt from a Con-Ed document, the 4kv stuff is primarily over-head / radial in nature: