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Newly Posted Transformer Drawings #177997
05/21/08 02:13 AM
05/21/08 02:13 AM
Scott35  Offline
OP
Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Regarding the most recently posted Transformer Drawings in the Technical Reference area:

Please address any questions, comments or etc. regarding these new drawings to this thread.

I am curious if the drawings are clear enough and concise at the same time.

Drawings of reference are:

SDS Transformer Grounding

4 Wire Open Delta

4 Wire Closed Delta

Corner Grounded Delta

Center Tap Grounded Delta

Ungrounded Delta
***Addressed in separate thread, located at:
https://www.electrical-contractor.n...showflat/Number/177996/page/1#Post177996

3 Phase 4 Wire Wye

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Tools for Electricians:
Re: Newly Posted Transformer Drawings [Re: Scott35] #186942
06/06/09 01:17 AM
06/06/09 01:17 AM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,250
SI,New Zealand
Thanks for the drawings Scott.
One question, we don't use the Open Delta configuration over here, what advantage does it have over the closed delta configuration?

Re: Newly Posted Transformer Drawings [Re: Trumpy] #186944
06/06/09 03:18 AM
06/06/09 03:18 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
Open delta saves the poco one transformer.
It is really pretty common around here.
This is the typical installation. The 50KVA is the center tapped one and serves the single phase 120/240v loads in addition to the 240v 3p loads. The 25kva is the wild leg (208 to ground) and only serves 3p loads.

[Linked Image]


Greg Fretwell
Re: Newly Posted Transformer Drawings [Re: gfretwell] #186988
06/09/09 10:05 PM
06/09/09 10:05 PM
Scott35  Offline
OP
Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
As Greg described, it saves the Poco one Transformer.

In my areas, I see Open Delta setups for 3 Phase 3 Wire Services, and 3 Phase 4 Wire Services.

The Open Deltas are commonly used where the demand is low (like a peak demand lower than 25 KVA), however I have seen some large 3 Phase, 3 Wire Open Delta setups for Industrial Customers, where the Nominal Demand was in the 100 KVA range.
These setups had Two 167 KVA Pole Mounted Single Phase 120/240V Transformers, spaced on either side of the Pole (similar to Greg's posted Image).
Those setups appeared as if they are anticipating adding a Third Pot later.
There was no indication of an original Closed Delta configuration, where the Center Pot had been removed (due to failure, or another reason).
I will search my Archives for images of those Industrial setups.

Scott


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Newly Posted Transformer Drawings [Re: Scott35] #186995
06/09/09 10:59 PM
06/09/09 10:59 PM
Scott35  Offline
OP
Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Forgot to mention:

LADWP (Los Angeles Department of Water & Power) used Open Delta setups quite commonly in areas zoned for Commercial + Residential Customers.
This would be in areas where there are both Commercial Customers + Residential Customers on the same Transformer(s).

There were some areas where the physical sizes of the Transformers on the Open Deltas, were noticeably different.
For example, the "Main" Transformer (the one with the Center Tap of the Secondary being used), would be very large, in comparison to the "Kicker" Transformer (the Transformer used for the "Top Of The Delta").
Sizes such as 75 KVA "Main" / 15 KVA "Kicker" were common in certain areas.

Some of the LADWP Open Delta Pole arrays exist today. Most have been eliminated during a Building's Alteration, in favor of a 4 Wire Wye derived from a Pad Mounted transformer.

Additionally, where Primary Distribution + Secondary Feeders have been placed in Underground Ducts, the resulting affects call for Pad Mounted Transformers, or large Transformers in Underground Structures.

UGS's are very common for Primary Voltages of 34,500V, with Secondary Voltages of 480Y/277 - 600V, and Capacity of >750 KVA (2500 KVA, 3750 KVA,).

So, to sum up the response to your question; the Open Delta "Vee" (as shown in Greg's image), is a Cost-Effective method for Pocos to deliver 3 Phase Service to Customers, where the Demand is low.

The Demand may be 3 Phase 3 Wire, Single Phase, or 3 Phase 4 Wire.
Specifically, the concept was to deliver 3 Phase Service to a Customer, whom had a small 3 Phase Demand, and a nominal 1 Phase Demand.

Example:
* (2) 5 HP 3 Phase Motors,
* (1) 7.5 HP 3 Phase Motor,
* 20 KVA @ 240V 1 Phase 3 Wire Demand.
* 3 Phase Motors are Non-Coincidental Loads: One normally runs alone, however, Two may run at same time for less than 15 Minutes.
Any Single Motor may run >180 Minutes at a given time.

Another use of an Open Delta is the "TEE" connection.
These are used for 2 Phase Systems, and where a low power 208Y/120V 3 Phase 4 Wire SDS (Separately Derived System) is installed.

The 2 Phase Systems are illustrated in the Technical Reference section, according to the type of SDS obtained.
These are "TEE" Connections for Open Delta setups.
For Closed setups, they are "Taylor" and similar.

Per the 208Y/120V 3 Phase 4 Wire "Open Delta TEE", many of the Dry-Type Transformers rated 15 KVA and less, will be Open Delta TEE arrangements.
This eliminates one full Primary & Secondary winding, yet still yields an output consisting of any of the following:

* 208V 3 Phase - 3 Wire;
* 208V 1 Phase - 2 Wire: from L1-L2, L2-L3, or L1-L3;
* 120V 1 Phase 2 Wire: from L1-N, L2-N, or L3-N;
* 120V 1 Phase 3 Wire (Multiwire): from L1/L2-N, L2/L3-N, or L1/L3-N;
* 120V 1 Phase 4 Wire (Multiwire): from L1/L2/L3-N.

Input may be from any 3 Phase 3 Wire available, such as:

* 200V (208V),
* 230V (240V),
* 380V,
* 416V,
* 460V (480V),
* 575V (600V),
* 120V,
* 220V.

Scott



Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Newly Posted Transformer Drawings [Re: Scott35] #186996
06/09/09 11:05 PM
06/09/09 11:05 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,298
Estero,Fl,usa
The only place I have actually seen center tapped delta with 3 transformers is behind the Hog's Breath Saloon in Key West.
It is strange to me since most of the load still appears to be single phase if you look at all of the drops.
(several buildings being served single phase)
This is the wild leg connection (foreground).
[Linked Image]


Greg Fretwell
Re: Newly Posted Transformer Drawings [Re: gfretwell] #187005
06/10/09 08:26 AM
06/10/09 08:26 AM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,250
SI,New Zealand
Hey,
Great stuff, guys.
Will have a read through in the morning when I am more awake.

Re: Newly Posted Transformer Drawings [Re: gfretwell] #187182
06/16/09 06:38 PM
06/16/09 06:38 PM
W
wa2ise  Offline
Member
Joined: Nov 2002
Posts: 787
Oradell NJ USA
Originally Posted by gfretwell
Open delta saves the poco one transformer.
It is really pretty common around here.
This is the typical installation. The 50KVA is the center tapped one and serves the single phase 120/240v loads in addition to the 240v 3p loads. The 25kva is the wild leg (208 to ground) and only serves 3p loads.

[Linked Image]


[Linked Image]

Do power companies follow a rule or a convention as to which phases in your open leg panel is across the 2nd transformer, and which set of phases bridges the open leg? In the diagram, it shows the 2nd transformer as between phases B and C, and the open between A and B. If the phase rotation is always ABC, could one say that the power company always places the 2nd transformer between B and C and never A and B, or is it random? In this case, I will always call the wild leg "phase B" at the particular building I'm in. I realize that one transformer set up on one pole would be say ABC, and one down the street a ways may be BCA, and yet further down the road CAB, to keep the poco power plant equally loaded on all phases.


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