2 Phase 4wire

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2-phase, 5-wire service

2-phase, 5-wire service

ok, trying this out with one jpeg since it looks like max file size is less than 150kb. may have to post a couple followups for the rest....
 
2-phase, 5-wire service

2-phase, 5-wire service

first one was general view of incoming service going to C/T cab and then to disconnect.

here is the C/T cab....
 
2-phase, 5-wire service

2-phase, 5-wire service

and finally the main distribution panel....I think Ben Franklin himself was the EC on the job....
 
gravy said:
I'm trying like heck to not continue this as I'm sure we all have actual work to do, but:

I've never seen a panel like this with 4 busses plus a neutral....do they even still make them? I guess they need to make it bulletproof so nobody could ever install a 3-phase breaker by accident? All breakers would be 2-pole from this panel (either across A-B or C-D busses)? And all lighting and receptacle panels would be 1-ph, 3-wire loadcenters?

thanks again for all this info....big fan of the site (more of a lurker though).
Click to expand...
I'm not sure about new ones. These folks claim to retrofit them:
http://www.pennpanel.com/html/retrofit.html
 
gravy said:
thanks wayne- are you really saying that I can specify as part of my Tenant work a transformer (the Scott T is also new to me.....man I feel like a freshman at college again 20-years ago....just without the mullet) that will essentially turn my service into a 120/240V, 3-phase system where I can supply 120V 1-phase, 240V 1-phase, and 240V, 3-phase loads? I just googled this and it looks like a strange arrangement with a 50% tap on one winding and an 86.6% tap on the other. my overall building load (NEC connected) is 120 KVA.....do they make a 112KVA or 150KVA size for this as a standard?

I have been trying to post a couple JPEG's but have not been successful....any tips on how to do this?

thx
Click to expand...
Here are the connections for 3, 4, and 5 wire:
2-phaseConnections.jpg
 
Gravy,

Sorry I didn't reply to your PM til now. Attached are pictures of a service we changed out in philladelphia. We just converted the whole building to 3 phase with the scott t. It was a whole lot cheaper then messing with the existing 2 phase. We bought the transformer through colonial electric. Let me know if I can be of any help.

Steve
 
hurk27 said:
Oh but please keep this thread going, I would love to hear the outcome of this one. never ran into a 2 phase feeding a building before, just old draw bridges, and we used a Scott-T to get 3 phase to power the new drive motors when they up graded the drive.:D

Oh and pleanty of photos is a must:D
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Wayne,
There is a "T" connection and a "Scott" connection. Using the term "Scott -T" can be confusing because they are two different type connections.

In the "T" connection, we don't need 86.6% transformer taps. One transformer primary is connected A-N and the other transformer primary is connected B-C.

For the 5-wire: From the primary A-N we transform to the secondary 1-3 and from the primary B-C we transform to the secondary 2-4. N is the secondary mid-points.

For the 3-wire case: From the primary A-N we transform to the secondary 1-N and from the primary B-C we transform to the secondary 2-N.

While the "T" connection can use standard transformers, it has unbalanced 3-phase primary currents. The Scott connection uses a "main" and "teaser" transformer to solve the unbalance problem.
 
2-phase, 5-wire

2-phase, 5-wire

Thanks everybody for posting this info...I'm a hell of a lot smarter today than I was yesterday (problem is I had to delete other key info in my brain to accept the new info....I wonder what that was....):D
 
Thanks for the interesting post.

See if you can get some internal shots of the panel in post #24. It looks like some 4-wire and 2-wire fuse blocks. Get some close-ups of the connections & bus-work if you can.

Not many of us get to see this stuff.
 
About a year ago, I ran into existing 2-ph power at a site and was getting lost in the coversions and misinformation out there. Fortunately the client changed their mind about what they wanted to do and I was able to put in a new 400A single phase service (only 2phases present on the pole).

I found out that next month the client wants to move into and rehab that building that has the existing 2ph 240 w/ a center tapped phase for 120. Looks like I'll be revisiting this stuff again soon. I'm pretty sure they have 3-phase equipment... :(
 
lakee911 said:
About a year ago, I ran into existing 2-ph power at a site and was getting lost in the coversions and misinformation out there. Fortunately the client changed their mind about what they wanted to do and I was able to put in a new 400A single phase service (only 2phases present on the pole).

I found out that next month the client wants to move into and rehab that building that has the existing 2ph 240 w/ a center tapped phase for 120. Looks like I'll be revisiting this stuff again soon. I'm pretty sure they have 3-phase equipment... :(
Click to expand...
??? You should have 170 volts phase-phase if you have 120 volts to the common on a 2-phase.

On 2-phase it is:
V12 = sqrt(V1^2 +V2^2)
 
mivey said:
Here are the connections for 3, 4, and 5 wire:
2-phaseConnections.jpg
Click to expand...
Questions:

What are the series inductors and resistors in two of the primary conductors?

Can these setups be used in either direction, i.e., 3ph to 2ph or 2ph to 3ph?

Do these connections allow full use of the transformers' total power ratings?
 
LarryFine said:
Questions:

What are the series inductors and resistors in two of the primary conductors?
Click to expand...
Those are some engineering symbols used to designate the impedance of the conductors.

Can these setups be used in either direction, i.e., 3ph to 2ph or 2ph to 3ph?
Click to expand...
Yes they can.

Do these connections allow full use of the transformers' total power ratings?
Click to expand...
Yes.
 
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LarryFine said:
Questions:

What are the series inductors and resistors in two of the primary conductors?

Can these setups be used in either direction, i.e., 3ph to 2ph or 2ph to 3ph?

Do these connections allow full use of the transformers' total power ratings?
Click to expand...
The series inductors and resistors are for a simple single-phase transformer model consisting of an ideal transformer and a series impedance.

The more complex model has a series impedance on the low & high side representing the leakage impedances. It also has a parallel combination of a resistor and inductor across the high side winding to represent the core losses and magnetizing current.

In the simple model, the assumption is that the current in the magnetizing branch is relatively small as compared to the total current and so the magnetizing branch is eliminated. Also for simplification, the low side impedance is transferred to the high side. This leaves us with a simple model having an ideal transformer with a series impedance on the high side.

As Jim said, they work in either direction.

These transformers are specially built to carry 15.5% more current than a standard single-phase transformer of the same kVA rating.
 
singledad234 said:
Is there a book or a web site i can more information on this??
Click to expand...
You can Google: "two phase" power
as a start. There are many old books that have been archived online that touch on this subject. Look for those in the late 1800's and early 1900's.

A have quite a few utility reference books and textbooks that cover the subject but not many are in print anymore and are not old enough to be scanned copyright free.
 
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