Utility upgrade from 4.16kv to 13.8kv.

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peter d

peter d

Senior Member
Location
New England
The utility in my area is doing some upgrading from 4.16kv to 13.8kv. They are changing out the poles completely and building the whole new set of distribution above the old stuff, then cutting it over.

Anyway, there is a 3-phase spur that runs into my neighborhood to power a large pumping station a few blocks over. Rather than covert that to 13.8 for this spur, they hung some 13.8 to 4.16kv transformers on the side street where the spur enters the neighborhood. :blink: Now, I know the reason they did this is cost, but it seems like it would have made more sense to just upgrade the transformer at the pumping station, and replace a half mile of poles and hardware. Now, they have another set of transformers as a failure point. Can any utility guys shed light on this?
 
peter d said:
The utility in my area is doing some upgrading from 4.16kv to 13.8kv. They are changing out the poles completely and building the whole new set of distribution above the old stuff, then cutting it over.

Anyway, there is a 3-phase spur that runs into my neighborhood to power a large pumping station a few blocks over. Rather than covert that to 13.8 for this spur, they hung some 13.8 to 4.16kv transformers on the side street where the spur enters the neighborhood. :blink: Now, I know the reason they did this is cost, but it seems like it would have made more sense to just upgrade the transformer at the pumping station, and replace a half mile of poles and hardware. Now, they have another set of transformers as a failure point. Can any utility guys shed light on this?
Click to expand...
If yours was the only spur they were dealing with then converting would make sense. Cost, time, resources all play a role. How do you eat an elephant?

Add: transformers are not that big of a failure point. The recently installed step-down is probably one of the lower probability failure points given the age of what is beyond it at this point.
 
half mile of poles and hardware

gotta believe that is way more expensive than a transformer change out, they do not 'throw away' the 4.16 xfmr.
Probably even way cheaper factoring in the year to year losses in the transformer core.

May also be right of way or clearance issues.
Been 50 years since worked for a POCO, but recall having to do a new survey for similar line upgrade, not an issue of 'just' planting new poles. Even had to have public hearings and prepare presentations for the public to comment on and endlessly kibitz about, much worse now than in mid 60's.

PSE is trying to upgrade a 69 kV major distribution line here, lots of public resistance (pun intended) for any changes, some of it due to folks all lathered up by emi fears, etc...etc... It has been 2 YEARS since the PSE effort started.
 
No doubt cost is the issue. But if the goal is to eliminate the 4.16kv, why don't they just do it already? :p As you might expect, the 4.16kv infrastructure is ancient and the poles supporting it are well past their life span. They are also undersized (diameter) and too short.

As a side note, they have installed 2.4/7.2kv transformers all over my local area, for obvious reasons.
 
They upgraded from 4.16 to 13.8 most likely due to demand/expansion downstream

on your spur load is most likely light for 4.16 so why change it?
if they went to 13.8 all the current service 120/240 xfmrs would need changed out
not sure those are std (but definitely more exp 5kv clas to 15kv)

most likely available fault i would increase also
 
A few reasons:

1. If the 4.16kv poles are still in good shape and not over loaded, it will cost more to replace them than setting down a few jumbo pigs, which chances are might actually have been recycled from another location that got upgraded.


2. If the pumping station transformer has a delta secondary, a major headache is averted. For most POCOs the internal rules are wye primary wye secondary, so changing that transformer would require the customer to upgrade his service.

3. A lesser degree as mentioned already might be fault current, though I doubt it.
 
The reason is not fault i
but an unintended consequence
the reason is the existing is suitable for the load

the fact that you have 3 ph in a residential neighborhood implies excess capacity
1/2 mile perhaps 50 houses or so

are the pumps 4160?
 
peter d said:
No doubt cost is the issue. But if the goal is to eliminate the 4.16kv, why don't they just do it already? :p As you might expect, the 4.16kv infrastructure is ancient and the poles supporting it are well past their life span. They are also undersized (diameter) and too short.

As a side note, they have installed 2.4/7.2kv transformers all over my local area, for obvious reasons.
Click to expand...

The goal is not so much to get rid of 4.16kv (though that certainly is happening) but rather rid of the ageing assets and reduced capacity associated with 4.16kv. For most POCOs 5kv construction stopped in the 70s, so anything remaining today is at least 40 years old. I say at least, because 4.16kv half the time is a byproduct of conversion from the 2.4kv delta days. Granted a pole pig can last over 100 years, but to POCOs they are considered disposable assets sized to last about 30 to 40 years.

Even if the 4.16kv system itself happens to be in good condition, there is still the issue of the infrastructure feeding it (which often happens to be even older). As one would guess, most 4.16kv systems were fed by much smaller local substations (of about 6 to 15MVA capacity) fed by what are now considered none-standard sub-transmission voltages like 26.4kv and 27.6kv. Some are lucky in that they used 12, 22 and 33kv since these are now close to common standards. And, consider that 27.6kv is fed by gear and transformers as well, making a 3rd group is ageing none standard assets.


POCOs typically go about this in two ways:


1. Pick a new official distribution voltage higher than 5kv like 13.8kv. Expand and set down new 40MVA, 50 or 60MVA transformers next to the older 115 to 27.6kv transformers at the sub-transmission supply substation. Draw out new 13.8kv trunk lines connecting all new loads to them. The 4.16kv system is slowly upgraded with reaming segments taken off the older 27.6 to 4.16kv intermediate substations via jumbo pole pigs with the 27.6kv system is gradually taken out of service and removed.


2. Turn the sub-transmission system into the distribution system. This is far more economical provided the sub-transmission system is still in good shape. The existing 115kv-23kv transformers are solidly grounded at the supply substation and a neutral is run along with sub-transmission poles. This is actually how a lot of our distribution voltages came about. 3 wire 12kv delta sub-transmission went 7.2/12.47kv Y, 22kv sub-transmission went to 13.2/23kv distribution and 33kv went to 19.2/34.5kv. Like this new construction could tap right off existing sub-transmission circuits and new transformers could be added at the 115kv stations as needed without having to worry about the existing combination. Adding a 3rd 60MVA delta wye transformer is a LOT easier when the other two units are of the same voltage, impedance and vector group. In fact, the two older units could be rated 40MVA while your new unit is rated 60MVA, as long as all have equal impedances & tap settings the load will divide evenly in proportion to the Kva rating. The 2nd 40 MVA can be replaced when it finally reaches its useful life 5 years latter with a new 60MVA, and then the 3rd 10 years latter. Then the buss and breakers can be replaced over a period of 4 years. New 23kv busses and breakers can come right off the existing. Now comparing that to literally doubling the size of the station, expanding the 115kv bays, new 115kv transformers (more than one in case the other fails since the existing will be of no help), new 13.8kv gear, control ect makes for a more expensive upgrade- provided the 27.6 isn't in dire need of immediately being pulled out of service. As the 23kv sub-transmission poles near capacity- or a single sub-trans circuit going out will results in to many customer being offline, new 23kv circuits a drawn out and connected to the 23kv system thats replacing the 4.16kv system. The same happens with the intermediate stations being removed and jumbo pigs feeding the remaining segments.
 
Ingenieur said:
The reason is not fault i
but an unintended consequence
the reason is the existing is suitable for the load

the fact that you have 3 ph in a residential neighborhood implies excess capacity
1/2 mile perhaps 50 houses or so

are the pumps 4160?
Click to expand...

I disagree, it can be in some cases.
 
Maybe they plan to upgrade that spur in the next quarter. From a utility standpoint usually they try to keep voltages on a feeder the same. That new bank is in fact a possible failure point, although not probable. Mounting a 13.8 > 4160 bank at the dead end for the pumping station, would be the normal thing to do in that situation. Unless however, the pumping station, has a riser pole and an underground service lateral with a padmount. In that case I can see the need or reasoning behind installing the extra transformers.

Sent from my VS986 using Tapatalk
 
Ingenieur said:
if the main mva capacity is increased
and the branch is increased
can't see how sc mva would not
Click to expand...

It would increase, hence why a utility might not want to upgrade the branch. Perhaps it wasn't the best example as I doubt thats the case here, but you its not impossible.
 
Ingenieur said:
They upgraded from 4.16 to 13.8 most likely due to demand/expansion downstream

on your spur load is most likely light for 4.16 so why change it?
if they went to 13.8 all the current service 120/240 xfmrs would need changed out
Click to expand...

Almost all the cans around here are dual voltage 7.2/2.4 with the tap changer switch on the side.

Ingenieur said:
are the pumps 4160?
Click to expand...

480Y277 service at the station.
 
Ingenieur said:
the fact that you have 3 ph in a residential neighborhood implies excess capacity
Click to expand...

Not sure what you mean by this. The 3-phase goes into the neighborhood solely for this pump station, as the pump station in the back end of the lowest part of this cluster of houses. The 3-phase serves no other loads other than the regular 120/240 along the way. This is common where I live, and probably everywhere else in the country. Whenever I see 3-phase heading into an area that I know is all residential, I know there is a pump station at the end of it.
 
mbrooke said:
A few reasons:

1. If the 4.16kv poles are still in good shape and not over loaded, it will cost more to replace them than setting down a few jumbo pigs, which chances are might actually have been recycled from another location that got upgraded.


2. If the pumping station transformer has a delta secondary, a major headache is averted. For most POCOs the internal rules are wye primary wye secondary, so changing that transformer would require the customer to upgrade his service.

3. A lesser degree as mentioned already might be fault current, though I doubt it.
Click to expand...

mbrooke said:
The goal is not so much to get rid of 4.16kv (though that certainly is happening) but rather rid of the ageing assets and reduced capacity associated with 4.16kv. For most POCOs 5kv construction stopped in the 70s, so anything remaining today is at least 40 years old. I say at least, because 4.16kv half the time is a byproduct of conversion from the 2.4kv delta days. Granted a pole pig can last over 100 years, but to POCOs they are considered disposable assets sized to last about 30 to 40 years.

Even if the 4.16kv system itself happens to be in good condition, there is still the issue of the infrastructure feeding it (which often happens to be even older). As one would guess, most 4.16kv systems were fed by much smaller local substations (of about 6 to 15MVA capacity) fed by what are now considered none-standard sub-transmission voltages like 26.4kv and 27.6kv. Some are lucky in that they used 12, 22 and 33kv since these are now close to common standards. And, consider that 27.6kv is fed by gear and transformers as well, making a 3rd group is ageing none standard assets.


POCOs typically go about this in two ways:


1. Pick a new official distribution voltage higher than 5kv like 13.8kv. Expand and set down new 40MVA, 50 or 60MVA transformers next to the older 115 to 27.6kv transformers at the sub-transmission supply substation. Draw out new 13.8kv trunk lines connecting all new loads to them. The 4.16kv system is slowly upgraded with reaming segments taken off the older 27.6 to 4.16kv intermediate substations via jumbo pole pigs with the 27.6kv system is gradually taken out of service and removed.


2. Turn the sub-transmission system into the distribution system. This is far more economical provided the sub-transmission system is still in good shape. The existing 115kv-23kv transformers are solidly grounded at the supply substation and a neutral is run along with sub-transmission poles. This is actually how a lot of our distribution voltages came about. 3 wire 12kv delta sub-transmission went 7.2/12.47kv Y, 22kv sub-transmission went to 13.2/23kv distribution and 33kv went to 19.2/34.5kv. Like this new construction could tap right off existing sub-transmission circuits and new transformers could be added at the 115kv stations as needed without having to worry about the existing combination. Adding a 3rd 60MVA delta wye transformer is a LOT easier when the other two units are of the same voltage, impedance and vector group. In fact, the two older units could be rated 40MVA while your new unit is rated 60MVA, as long as all have equal impedances & tap settings the load will divide evenly in proportion to the Kva rating. The 2nd 40 MVA can be replaced when it finally reaches its useful life 5 years latter with a new 60MVA, and then the 3rd 10 years latter. Then the buss and breakers can be replaced over a period of 4 years. New 23kv busses and breakers can come right off the existing. Now comparing that to literally doubling the size of the station, expanding the 115kv bays, new 115kv transformers (more than one in case the other fails since the existing will be of no help), new 13.8kv gear, control ect makes for a more expensive upgrade- provided the 27.6 isn't in dire need of immediately being pulled out of service. As the 23kv sub-transmission poles near capacity- or a single sub-trans circuit going out will results in to many customer being offline, new 23kv circuits a drawn out and connected to the 23kv system thats replacing the 4.16kv system. The same happens with the intermediate stations being removed and jumbo pigs feeding the remaining segments.
Click to expand...

Awesome info. :cool::thumbsup:
 
If only I had done google street view in the first place, I would have answered my own question. :slaphead: Looks like the pump station has a 480 volt delta secondary. Now I see why they didn't want to upgrade this, that would have necessitated a switch gear change at the station.
 
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