can 2 Bucket Transformers share a neutral? House to house backup generator circuit.

[mivey]

what is the difference between the LTC and voltage regulator, besides the percentage difference mentioned?

The LTC is integrated with the main transformer. The regulator is a separate stand-alone unit.

The LTC is like using a bus regulator where the whole station has the same output voltage. Okay when loads are balanced but I don't like it. I prefer single-phase feeder regulation where each feeder is adjusted based on load as is each phase.

 

[electrofelon]

The LTC is integrated with the main transformer. The regulator is a separate stand-alone unit.

The LTC is like using a bus regulator where the whole station has the same output voltage. Okay when loads are balanced but I don't like it. I prefer single-phase feeder regulation where each feeder is adjusted based on load as is each phase.

Cool, thanks.

 

[mbrooke]

An auto needs to keep the same configuration. delta-delta or wye-wye but not a mix.

You could certainly use an autotransformer but I'm sure it would be odd for distribution levels. Autotransformers are used in transmission stations

Not odd around here, often used when going from 23kv to 13.8kv, or 13.8kv to 13.2 or 12.47. I think its even now appearing when stepping down to ungrounded systems.

 

[mbrooke]

Here in upstate ny it's the land of 4800 delta distribution. Often you will see transformer plarforms that are fed from a newer 13.2/7.62 line and feeding the older 4800 lines. I used to wonder if they were auto or isolation banks, but after careful looking, all the ones I have been able to trace out are isolation. What would be the implications of using autos in this situation? Clearly, the originally ungrounded 4800 would have the ground reference from the 13.2 MGN system.

You can use an auto no issues, however nuisance fuse blowing may increase because any temporary L-G faults will cause greater currents to flow.

 

[mbrooke]

Yes, but they make relatively small changes in voltage, not a large change like a step-down bank.

Load Tap Changers (LTC) are usually a few percent, like +/- 2.5 and 5 percent. Voltage regulators are usually +/- 10 percent with something like 32 steps.

add: the no-load TCs are usually +/- 2.5 & 5 percent. The on-load TCs are +/- 10% in 32 steps

I'm sure you've seen this before, but for the readers. An auto transformer, but with taps and an LTC:

 

[electrofelon]

I'm sure you've seen this before, but for the readers. An auto transformer, but with taps and an LTC:

LOL, Fischer Price stuff:

Weight: 195,000 lbs
Main tank oil: 7156 gallons


Here is what (will) feeds my house. They just installed this new bank. The existing one is an old leaner just one pole down. Its surprising only 1500 KVA total, does a pretty big area. this is 4 miles from my house and goes another few miles after me. Rural area though.

ETA goes about a mile then splits to single phase, hits a voltage regulator after another mile.

 

[mbrooke]

LOL, Fischer Price stuff:

Weight: 195,000 lbs
Main tank oil: 7156 gallons

Ehhh, its on the smaller side, only 65MVA and auto transformer. Try 1,200MVA 22kv-500kv GSU (generator step up)

Here is what (will) feeds my house. They just installed this new bank. The existing one is an old leaner just one pole down. Its surprising only 1500 KVA total, does a pretty big area. this is 4 miles from my house and goes another few miles after me. Rural area though.

Typical setup. Looks like an isolation unit (2 winding) from here. There should be a name tag somewhere on the back of the trafo that you can take a pic from with a zoom lens. Should look something this:

 

[mivey]

Not odd around here, often used when going from 23kv to 13.8kv, or 13.8kv to 13.2 or 12.47. I think its even now appearing when stepping down to ungrounded systems.

What about from 13 to 4? Seems like those would be different but maybe not.

 

[mbrooke]

What about from 13 to 4? Seems like those would be different but maybe not.

It was isolation, delta-delta, but I think I'm seeing autos. Either that maybe its just wye-wye with a single primary and single secondary bushing.

 

[mivey]

I'm sure you've seen this before, but for the readers. An auto transformer, but with taps and an LTC:

I usually see those as an isolation unit. The HV autos are usually something like 500 kV to 230 or 115 kV or similar. Once below about 69 kV on the load side the HV units tend to be isolation units. Nothing engraved in stone about that though.

 

[mivey]

LOL, Fischer Price stuff:

Weight: 195,000 lbs
Main tank oil: 7156 gallons


Here is what (will) feeds my house. They just installed this new bank. The existing one is an old leaner just one pole down. Its surprising only 1500 KVA total, does a pretty big area. this is 4 miles from my house and goes another few miles after me. Rural area though.

ETA goes about a mile then splits to single phase, hits a voltage regulator after another mile.

Platforms used to be more popular, say in about the 167-250 kVA per phase range and up. Now it is a padmount unless just a necessity. We also used to see a lot of large pole-mounts on the ground either fenced (usually in an industrial site) or in a transclosure.

I like those platforms for line regulators though. Much better than hanging them on three poles.

 

[mbrooke]

I usually see those as an isolation unit. The HV autos are usually something like 500 kV to 230 or 115 kV or similar. Once below about 69 kV on the load side the HV units tend to be isolation units. Nothing engraved in stone about that though.

Yup, I always see wye auto (with sometimes a delta tertiary, but no always, topic all on its own) when going from 500 to 161, 345 to 115, 230-115, 115-69.

Often the reason why transmission levels are in multiples of 3 is because generally that tends to be the largest voltage difference where an auto transformer is reasonably practical. Ie Europe is big time 400kv-132kv, 500-161kv at TVA, and 345-115 or 345-138 making the bulk in many large swaths of the US.


Auto transfomers are less common when going from transmission to sub-transmission, but you do find them at times.

 

[mivey]

Ehhh, its on the smaller side, only 65MVA and auto transformer.

Using the buried tertiary help with the overvoltage on ground faults? Ever use one unburied for station service or something?

 

[mbrooke]

Using the buried tertiary help with the overvoltage on ground faults?

Not to my knowledge, but there is debate in the power industry over eliminating territary windings altogether in large auto transformers. I will post two links to a discussion on an engineering forum.

Ever use one unburied for station service or something?

Oh, I've seen them do just about everything. Seen them feed station load; seen them feed sub-transmission; seen them feed distribution through a reactor, zig-zag ground and voltage regulator; seen them feed an SVC for reactive power needs of the transmission network and/or voltage support at the station for N-1 contingencies.


Here is the SVC example:

 

[mivey]

Yup, I always see wye auto (with sometimes a delta tertiary, but no always, topic all on its own) when going from 500 to 161, 345 to 115, 230-115, 115-69.

Often the reason why transmission levels are in multiples of 3 is because generally that tends to be the largest voltage difference where an auto transformer is reasonably practical. Ie Europe is big time 400kv-132kv, 500-161kv at TVA, and 345-115 or 345-138 making the bulk in many large swaths of the US.


Auto transfomers are less common when going from transmission to sub-transmission, but you do find them at times.

Given that an auto tranformer is common for something like 14.4 to 7.2 kV, at what range would you think an isolation unit would be more common? I would expect something like 35 to 4 kV would be an iso but would have to read up on the pros and cons as the voltage spread changes. I usually hear the zero sequence blocking stuff and that can be a factor if you have accumulated a bunch of Z0 but I wonder what else makes the laundry list?

I have not seen a 115 to 35 kV auto until your pic.

 

[mbrooke]

Sorry for the blur, here is the zoomed in version. 220kv going down to 66kv.

 

[mivey]

Yup, I always see wye auto (with sometimes a delta tertiary, but no always, topic all on its own) when going from 500 to 161, 345 to 115, 230-115, 115-69.

Often the reason why transmission levels are in multiples of 3 is because generally that tends to be the largest voltage difference where an auto transformer is reasonably practical. Ie Europe is big time 400kv-132kv, 500-161kv at TVA, and 345-115 or 345-138 making the bulk in many large swaths of the US.


Auto transfomers are less common when going from transmission to sub-transmission, but you do find them at times.

From what they say, the delta gives a low-impedance path for I0 to circulate and helps control overvoltage on ground faults.

Perhaps 3 to 1 is the magic number that balances out the pros and cons? So 13 to 4 kV would be on the fence? Got to be a study on that somewhere.

 

[kwired]

What OP proposes does work. Might create some problems during abnormal conditions and some have mentioned codes being violated.

Unless you do switch the neutral with transfer switch you are going to have parallel path involving the EGC that was run with generator suppy circuit and the service neutrals/utility MGN. But if you don't run a neutral there is none to switch either.

I am in agreement with others in that one might be as well off to just buy another generator. Materials spent to go 600 feet will get you most of another generator or maybe even all of a cheap one from Harbor Freight.

 

[mbrooke]

From what they say, the delta gives a low-impedance path for I0 to circulate and helps control overvoltage on ground faults.

It is a zero sequence source, but do you really need it?


https://www.eng-tips.com/viewthread.cfm?qid=445842

There was another one but I need to hunt for it, toward the end there was a similar discussion of removing the territaries.

Perhaps 3 to 1 is the magic number that balances out the pros and cons? So 13 to 4 kV would be on the fence? Got to be a study on that somewhere.

Asked this same question a few months ago:

https://www.eng-tips.com/viewthread.cfm?qid=437627

 

[mivey]

It is a zero sequence source, but do you really need it?


https://www.eng-tips.com/viewthread.cfm?qid=445842

There was another one but I need to hunt for it, toward the end there was a similar discussion of removing the territaries.





Asked this same question a few months ago:

https://www.eng-tips.com/viewthread.cfm?qid=437627

Interesting.