is this supposed to be?

kwired

Electron manager
An attempt to get wye secondary voltages out of a two transformer system? If it actually worked I don't know why we wouldn't see those in the wild instead of high leg delta systems.
 

mbrooke

Senior Member
Your on the money, but I have no idea like you if it will work or if the left transformer needs to be of a special variety.
 

Hv&Lv

Senior Member
We have a couple of them installed on our system.
we call them bastard banks.

they work OK but not for big loads.

some things to remember with this bank..
kVA is 3/4 of nameplate
0 degree leg is 1/2 kVA of first pot
120 degree leg is 1/2 kVA of the other pot
and the other leg is 1/2 of the smallest pot. The voltage drop is two times normal VD, and the losses are doubled
 

kwired

Electron manager
We have a couple of them installed on our system.
we call them bastard banks.

they work OK but not for big loads.

some things to remember with this bank..
kVA is 3/4 of nameplate
0 degree leg is 1/2 kVA of first pot
120 degree leg is 1/2 kVA of the other pot
and the other leg is 1/2 of the smallest pot. The voltage drop is two times normal VD, and the losses are doubled
What is the advantgage of using them? Advantage of a real wye system is ability to balance things.

Advantage of open delta is less primary conductors and infrastructure to what is usually a limited load and still have three phase secondary.

If you absolutely need 208 volts for a particular load then why not use a buck/boost transformer for that load?
 

mbrooke

Senior Member
Yes, we have a yard full of them
Well, I learned something new today. If someone said take yard full of standard pigs and make me a 120/208Y out of two pots I'd laugh. Now I stand corrected :happyyes::happyyes: Go you!
 

Hv&Lv

Senior Member
What is the advantgage of using them? Advantage of a real wye system is ability to balance things.

Advantage of open delta is less primary conductors and infrastructure to what is usually a limited load and still have three phase secondary.

If you absolutely need 208 volts for a particular load then why not use a buck/boost transformer for that load?
We have one built that feeds one small motor for hvac at a camp. It’s back in the woods about 6 miles. We have Vee phase (two lines of three phase) in there now, it’s been that way for years.
bottom line is cost. It was cheaper to pull three wires instead of four when it was originally built.
we won’t do it now.

BTW, that line is due for upgrades. When we reconductor it we will pull in new three phase and new neutral.
the good thing here is the camp can shut down for three weeks so we can do this dead. More savings. This help drive our decision to include the fourth wire and retire this particular bank.

the rest will be retired eventually. I think we have four not counting this one.
 

synchro

Senior Member
In the schematic that you posted above the A and B outputs are of course produced by 2/3 of the normal wye-wye transformer connection.
Phase C is being synthesized at the transformer secondaries just like in my post at the following link:

https://forums.mikeholt.com/forum/active-forums/electrical-calculations-engineering/2546600-1-ph-to-3-ph-converter#post2546705

In your schematic, the necessary inverted versions of A-N and B-N are produced by the reverse polarity connections of X4,X3 and X3,X2 respectively.
 

mbrooke

Senior Member
In the schematic that you posted above the A and B outputs are of course produced by 2/3 of the normal wye-wye transformer connection.
Phase C is being synthesized at the transformer secondaries just like in my post at the following link:

https://forums.mikeholt.com/forum/active-forums/electrical-calculations-engineering/2546600-1-ph-to-3-ph-converter#post2546705

In your schematic, the necessary inverted versions of A-N and B-N are produced by the reverse polarity connections of X4,X3 and X3,X2 respectively.

But wouldn't the voltage be zero... ok... I kind of get it. Kind of. The phase displacement being 120* however I can't picture.
 

kwired

Electron manager
We have one built that feeds one small motor for hvac at a camp. It’s back in the woods about 6 miles. We have Vee phase (two lines of three phase) in there now, it’s been that way for years.
bottom line is cost. It was cheaper to pull three wires instead of four when it was originally built.
we won’t do it now.

BTW, that line is due for upgrades. When we reconductor it we will pull in new three phase and new neutral.
the good thing here is the camp can shut down for three weeks so we can do this dead. More savings. This help drive our decision to include the fourth wire and retire this particular bank.

the rest will be retired eventually. I think we have four not counting this one.
We have lots of limited loads both along the main lines and in isolated areas. If three phase is needed open delta is what is used. What is the advantage of this particular setup over the open delta?

Small motors probably get phase conversion equipment in isolated areas with single phase only being what is readily available from POCO.
 

Hv&Lv

Senior Member
We have lots of limited loads both along the main lines and in isolated areas. If three phase is needed open delta is what is used. What is the advantage of this particular setup over the open delta?

Small motors probably get phase conversion equipment in isolated areas with single phase only being what is readily available from POCO.
120/208

like I say, we wouldn’t build it now as most motors now are 208/230
 

kwired

Electron manager
120/208

like I say, we wouldn’t build it now as most motors now are 208/230
I don't find that to be much advantage on most the limited load installs I ever been around.

As far as three phase motors go, many today are marked 208/230, but in past was common to just see 240 only marked on them.

Like I said earlier an advantage to a true wye system is the ability to balance 120 volt loads on it, but this system can't be balanced anyway and actually would be more tricky to try to load it to what it can handle per leg than to balance a real wye system.

Only advantage I see is if you actually need 208 vs 240, but that can also be fixed with buck/boost.
 

mbrooke

Senior Member
In the schematic that you posted above the A and B outputs are of course produced by 2/3 of the normal wye-wye transformer connection.
Phase C is being synthesized at the transformer secondaries just like in my post at the following link:

https://forums.mikeholt.com/forum/active-forums/electrical-calculations-engineering/2546600-1-ph-to-3-ph-converter#post2546705

In your schematic, the necessary inverted versions of A-N and B-N are produced by the reverse polarity connections of X4,X3 and X3,X2 respectively.
Is this similar to a T connection? Or the same thing?


 
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