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#116080 - 02/14/04 01:32 AM Old delta-delta xfmr bank
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England


Thanks to bjarney for the photo and following notes:

 Quote:
This "H-frame" transformer bank about 15 miles away is still standing although the buildings have been leveled. It seems to be a 240/120V 4-wire ∆ bank that served a multi-tenant light-industrial/retail building space, probably built in the late 50s/early 60s.

The disconnected 12kV open-link fused cutouts are visible in the upper-lefthand corner. It's easy to pick out the delta-primary arrangement. The lower six spans are fed by the bank secondary in a {winding/jumpering} confinguration that was very popular at the time. Each tenant had a 120/240V 1ø 3-wire 'lighting' meter, fed from the closer lower 3 secondary spans, and a 240V 3ø 3-wire delta 'power' meter from the farther lower three spans. On the 1ø spans, note the middle conductor looks smaller, for it is bare.

Note the conductor spans [12kV and 240V] are all solid copper, whereas if presently intalled, they would be stranded ACSR {aluminum conductor/steel-reinforced} unless in a high-corrosion area like on the seacoast.

Later 240/120V 3ø services are 4-wire ∆ served through 1 meter. Dual lighting and power metering [at differing rates] disappeared ~25 years ago.

I could not see any kVA rating stenciled on the transformer cans, although they would likely have been on the other {opposite} non-bracket side that was obscured by the mid-day sun. I would guess they are ±75kVA each, for a 225kVA bank. It is routine to have a somewhat larger center transformer for serving both 1 and 3ø, but apparenty that is(/was) not the case here. Nowadays, new 240/120V 3ø service is very limited—208Y/120 and 480Y/277V are the norm.

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#116081 - 02/14/04 03:12 AM Re: Old delta-delta xfmr bank
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
An interesting picture, and certainly like nothing you'd see in my part of the world.

I can make out the secondary links between the transformers and connecting to the 240V lines in delta configuration.

Why did the PoCo install two services run with separate 240 delta and 120/240 3-w feeders, rather than just running 4 lines to each building and then tapping off as needed for each meter?

The only reason I can think of is that with the 240 delta likely to be used for motor loads, using separate feeders could minimize the dimming of lights during the starting surges.

What's the significance of the yellow marker bands on the poles?

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#116082 - 02/14/04 11:39 AM Re: Old delta-delta xfmr bank
Nick Offline
Member

Registered: 08/13/01
Posts: 603
Loc: Riverside, CA
Paul
Around here the yellow bands just say High Voltage. In this case it looks like if someone got high enough they would already be in a world of trouble!

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#116083 - 02/14/04 12:05 PM Re: Old delta-delta xfmr bank
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Bjarney,
Thanks for submitting that picture, mate!.
You're quite right, the Primary Delta system can be easily seen there.
Just a small point, regarding what Nick mentioned about people climbing poles, this arrangment above, by virtue of how the wires on the bottom set of cross-arms, more or less provides it's own barrier to persons wanting to get a better look at the country-side.
BTW, are those transformers bonded together and Grounded?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#116084 - 02/14/04 02:05 PM Re: Old delta-delta xfmr bank
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Paul, I don't know the history of two sets of three conductors, even though indeed derived from a ‘4-wire’ source. The only clue I have is that local utility estimators would gripe about requests for wye-secondary transformer banks, for they could not serve any of the routine 'Edison three-wire' services from it. [Old habits die hard, I suppose.]

The yellow bands are most likely “Hi Signs” [lineman slang for ‘HIGH VOLTAGE’ signs] like the third item on www.techproducts.com/pg19.htm Their use probably evolved from a landmark legal case where some crazed idiot climbed a pole and got toasted.

Trumpy, I think the case-grounding practice has probably evolved along with secondary grounding—that is, used to be floating but now is rarely the case.

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#116085 - 02/14/04 04:14 PM Re: Old delta-delta xfmr bank
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Bjarney,
How are the connections made between the lines and the tails that feed the Xformers?
Are those Line-Tap nuts?, used over in the US?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#116086 - 02/14/04 04:45 PM Re: Old delta-delta xfmr bank
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
They're probably silicon-bronze split bolts—"bugs". With all the aluminum used nowadays, a mechanically-bolted "PG" [parallel-grooved] connector or hydraulically compressed "H-tap" is the norm.

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#116087 - 02/15/04 01:01 AM Re: Old delta-delta xfmr bank
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
I wondered if those yellow bands did just say HIGH VOLTAGE, but as Nick has said, it looks as though by the time anyone was high enough to see them properly he would already be surrounded by the primary lines linking down to the transformers.

Wonder what happened to that short cross board at the left-hand side? I have a vision of a utility worker needing a small piece of board for some reason and sawing it off the end!

 Quote:
The only clue I have is that local utility estimators would gripe about requests for wye-secondary transformer banks, for they could not serve any of the routine 'Edison three-wire' services from it.

More confirmation I suppose of just how firmly America adopted delta configurations for secondaries in earlier times.


[This message has been edited by pauluk (edited 02-15-2004).]

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#116088 - 02/15/04 04:03 AM Re: Old delta-delta xfmr bank
electure Offline

Member

Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
Good pic, Bjarney!

I believe the 2 sets of 3 wire feeders were installed so that the utility could meter the lighting and power loads separately.
Then they could charge different rates for each.

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#116089 - 02/15/04 08:26 AM Re: Old delta-delta xfmr bank
u2slow Offline
Member

Registered: 09/18/03
Posts: 198
Loc: Salt Spring, BC, Canada
This setup was commonly used around here(Vancouver, BC, Canada). One business I worked at several years ago still has this in place. I can also tell you that about 90% of additions over the years have been added to the lighting service

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