2-phase, 5-wire Thank You!

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gravy

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Just wanted to say thanks to the organizers of this forum for help resolving service voltage issue at a new retail store we just designed (attached link for original issue and threads). Quick summary: Our service from the POCO was a true 2-phase, 5-wire antiquated system. We wanted to re-use the service instead of having to heavy up the service which would have caused us to install a transformer vault within the store ($$$$). Luckily through this forum, I discovered the magical Scott T transformer (we affectionately call him Scotty now). We specified a custom built 200KVA Scott T transformer by Hammond Power which converted the incoming 2-phase, 5-wire service to a 208V, 3-phase, 4-wire service. The store opened on time and on budget thanks to Scotty. Attached photo of nameplate. Photos of the existing condition located on original thread.

Thanks Mike Holt and company....

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http://forums.mikeholt.com/showthread.php?t=116180&highlight=2-phase
 

glene77is

Senior Member
Location
Memphis, TN
Gravy,
Is there such a thing as 4 wire, 2 phase ?
Am guessing that there would be no neutral.
Have not been around enough to ever have seen a 2 phase anything.
 

Electric-Light

Senior Member
What was the lead time on it? Should the transformer fail/become damaged for whatever reason, how long before a replacement can be obtained?
 

rattus

Senior Member
Gravy,
Is there such a thing as 4 wire, 2 phase ?
Am guessing that there would be no neutral.
Have not been around enough to ever have seen a 2 phase anything.
Just connect the CTs of the 2-phase secondaries. This config has been called 4-phase, but that would start another long winded discussion so don't blab it around!. The CT is the neutral.
 

dicklaxt

Senior Member
This is all very interesting,,,,,,,,,,even tho I haved never been exposed to it,I was aware that it existed and was basically obsolete except for conditional services or applications.I do have a question tho,,,, what is considered the source when talking about the ground fault path and how will it be connected now that a Scott T transformer is in the mix?

dick
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
This is all very interesting,,,,,,,,,,even tho I haved never been exposed to it,I was aware that it existed and was basically obsolete except for conditional services or applications.I do have a question tho,,,, what is considered the source when talking about the ground fault path and how will it be connected now that a Scott T transformer is in the mix?

dick
The Scott T connection provides a Separatley Derived System, just like any other isolation transformer does.
 

kwired

Electron manager
Location
NE Nebraska
Does POCO use Scott T for 2 phase services?

Does POCO use Scott T for 2 phase services?

Does the POCO use Scott T to supply customer with 2 phase service?

I was always told there are no 2 phase distribution systems in the USA. But if there are 2 phase services they must convert from three phase systems to derive it. Otherwise an on site power source or customer owned conversion equipment would be required I would think.

Wouldn't it be better in the end to eliminate the two phase service - especially if there is no two phase loads to supply? Equipment would have to be custom made for each application and that could be expensive, not to mention down time if there is a failure of a component.
 

rattus

Senior Member
Never on a Sunday!

Never on a Sunday!

Wouldn't that be 5-wire?
Don't count too well on a Sunday. The answer is yes, the secondaries are not connected. There is no common conductor. There could be a reason for this, but I am too young to know what it might be. Have only seen it in books too.
 

hurk27

Senior Member
Does the POCO use Scott T to supply customer with 2 phase service?

I was always told there are no 2 phase distribution systems in the USA. But if there are 2 phase services they must convert from three phase systems to derive it. Otherwise an on site power source or customer owned conversion equipment would be required I would think.

Wouldn't it be better in the end to eliminate the two phase service - especially if there is no two phase loads to supply? Equipment would have to be custom made for each application and that could be expensive, not to mention down time if there is a failure of a component.

We had an old existing draw bridge that was a 2-phase motor that when the utility some time in the past changed to a poly phase (3-phase) system they installed a Scott-T transformer to keep this draw brige running, after many years of running like this and the motors were changed out to 3-phase motors, the utility changed out the transformers to regular delta supply, but we still have one draw bridge that has a Scott-T on the coustomer side to supply 3-phase from a 2-phase supply.
 

hurk27

Senior Member
We had an old existing draw bridge that was a 2-phase motor that when the utility some time in the past changed to a poly phase (3-phase) system they installed a Scott-T transformer to keep this draw brige running, after many years of running like this and the motors were changed out to 3-phase motors, the utility changed out the transformers to regular delta supply, but we still have one draw bridge that has a Scott-T on the coustomer side to supply 3-phase from a 2-phase supply.

Heres some photos off GE of the bridge first mention, the second bridge was removed and no longer exist
 

gravy

Member
What was the lead time on it? Should the transformer fail/become damaged for whatever reason, how long before a replacement can be obtained?
Hammond gave me a 4-week lead time for delivery. But now that you mention it, maybe I should have specified a spare.
 

gravy

Member
Gravy,
Is there such a thing as 4 wire, 2 phase ?
Am guessing that there would be no neutral.
Have not been around enough to ever have seen a 2 phase anything.
agreed....I had never seen or heard of a 2-phase service either. But they do still have some on the east coast apparently....this one was in philadelphia. They derive it on the utility side using multiple transformers with different tap settings (something to do with "more economically advantageous" back in the day = less transformers needed). By no means am I any kind of 2-phase expert even after going through this study. I hope I never meet this fellow again.
 

wireguru

Senior Member
I want to buy one of these scott-T transfomers so the next time I have some sound guy who wants '100 amps two phase 120 on its own leg with the ground lifted' instead of arguing I can just give it to him :grin:
 

PetrosA

Senior Member
I apprenticed near Philly back in the 80s and remember hearing about 2 phase systems, but the way they talked about them back then I thought there were already mostly dead and gone. I guess not...
 

kwired

Electron manager
Location
NE Nebraska
Two phase principles are not exactly dead. Most (probably all) single phase induction motors operate on the same principles as a two phase motor. You have at least two sets of windings with the voltage and current in each out of phase with the other(s) to create a rotating field. If the voltage and current in each set of windings were in phase with each other, the rotor would never develop any torque.
 
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