What type of pole mount transformer has one primary connector and four secondary connectors?

[mdlueck]

Greetings,

In Saint Joseph, MI.... the old downtown part of town I observe an unusual transformer configuration. They have AEP as their utility provider.

I see two sets of secondary on the poles. One is clearly USA standard 120/240.

The second set I would assume to be three phase delta 240v. However the transformer powering that bus has only a single connection to the primary, and four secondary connections. The middle two of the secondary are bonded together. Then a total of three wires connect to the bus it powers.

I would suspect three phase open delta. But I am puzzled at how the utility could make three phase anything with only a single primary connection!

We are in Consumers Energy territory of Michigan, and here the utility utilizes two standard 120/240 tubs to deliver three phase open delta. That configuration makes sense to me.

So is the AEP configuration even delivering a type of old three phase.... or a totally different output?

I am thankful,
Michael Lueck

 

[LarryFine]

Welcome to the forum.

It sounds like a dual-secondary unit that can be wired in parallel for 120v or in series for 120/240v.

In your case, they're in series, with the joined terminals forming the center-tap/neutral.

Most modern transformers are re-configured internally with jumpers when they're installed.

 

[mdlueck]

Greetings Larry,

hhhmmmm.... interesting. So if that is the case, then the utility ran two sets of 120/240 busses down the alley.... and they connect some customers to the "standard" 120/240 circuit while others get connected to the "special" 120/240 circuit?

"Ours is not to question why, simply flip and multiply." No wait, that is how to divide fractions!

Two sets of 120/240v busses, and no three phase for the business district!? Makes my head spin wondering what the designer was thinking 100+ years ago.

> Richmond, VA

ahhhh.... home of the beautiful Byrd Theatre and its wonderful WurlTzer organ!

The Mighty Wurlitzer Organ - Byrd Theatre

The Mighty Wurlitzer Organ is perhaps The Byrd’s most recognizable trademark and was designed as a “one-man0orchestra” to accompany silent movies.

byrdtheatre.org

We visited one, received a private tour, and I was allowed to play it.

I am thankful,
Michael Lueck

 

[ggunn]

...I am puzzled at how the utility could make three phase anything with only a single primary connection!

They can't

 

[zbang]

hhhmmmm.... interesting. So if that is the case, then the utility ran two sets of 120/240 busses down the alley.... and they connect some customers to the "standard" 120/240 circuit while others get connected to the "special" 120/240 circuit?

Not really, from the sound of it, there are two 120v windings brought out separately- connect the right end of one to the left end of the other and you have 240/120 with a center tap; connect both left ends and both right ends and you have double the power but only at 120v.

 

[LarryFine]

I'm confused now. There are more than three wires? Can you post pics?

 

[Hv&Lv]

Larry has it. We have some of these on our system also. Old transformers, but if they work well why scrap them.
It's single phase probably parallel services

 

[mdlueck]

I'm confused now. There are more than three wires? Can you post pics?

Next time I am out to Lake Michigan / Saint Joseph, I will take a photo.

For the immediate, I found this one which is close on-line. Only one primary bushing at the top as opposed to the two in the image.

The center two secondary bushings are bonded together.... and those are one of the three secondary connections. The other two secondary connections are the two outside secondary bushings.

 

[LarryFine]

The center two secondary bushings are bonded together.... and those are one of the three secondary connections. The other two secondary connections are the two outside secondary bushings.

Okay, then yes, it's what I said first: two secondaries in series.

I didn't understand your description of more than one set of wires.

 

[mdlueck]

Not really, from the sound of it, there are two 120v windings brought out separately- connect the right end of one to the left end of the other and you have 240/120 with a center tap; connect both left ends and both right ends and you have double the power but only at 120v.

Correct. But there are six secondary conductors running all the way down the alley behind the store fronts. I think it odd that both sets of secondary are 120/240v. I would have thought more likely single phase and three phase would make up the two secondaries.

At least in Consumers Energy territory, downtown what old poles are left and the lines not put underground.... then one secondary is 120/240v and the other set is 240v delta.

It was not uncommon 100 years ago to find the 240v delta secondary mounted on a cross arm of its own and not insulators down the pole.

I am thankful,
Michael Lueck

 

[LarryFine]

Correct. But there are six secondary conductors running all the way down the alley behind the store fronts. I think it odd that both sets of secondary are 120/240v. I would have thought more likely single phase and three phase would make up the two secondaries.

Do all of these wires connect to just this transformer?

At least in Consumers Energy territory, downtown what old poles are left and the lines not put underground.... then one secondary is 120/240v and the other set is 240v delta.

Have you looked end to end for another transformer(s)?

 

[mdlueck]

Do all of these wires connect to just this transformer?

The other secondary bus is powered by a smaller tub with three secondary bushings.... the usual 120/240v style.

Have you looked end to end for another transformer(s)?

Oh that would be odd.... to have another transformer powering the same bus at a completely different pole! That will take a return trip to Saint Joseph.

Still, with one tub connecting to all three secondary wires, I would not see how an additional transformer on another pole could also connect to the same three wires.

I am thankful,
Michael Lueck

 

[LarryFine]

The other secondary bus is powered by a smaller tub with three secondary bushings.... the usual 120/240v style.

Oh, I didn't realize you new that.

 

[kwired]

The other secondary bus is powered by a smaller tub with three secondary bushings.... the usual 120/240v style.

is there any interconnection between these two buses or are they completely separate and supplying separate loads?

Maybe different voltages? Would not be surprised if only one grounded conductor that is common to both secondary systems as well as to the primary system though.

Sometimes with overhead secondary there might be a controlled conductor that is for street lighting, need to follow these conductors and pay attention to what they connect to and you may answer some of your own questions.

Old farm places around here sometimes had five wires from the main pole to the house. Three was the 120/240 supply, two were three way traveler conductors from house to a three way switch on the pole for the light that was on the pole. That was pretty common back when those overhead conductors were hard drawn copper

 

[LarryFine]

is there any interconnection between these two buses or are they completely separate and supplying separate loads?

Perhaps a second transformer and corresponding lines were added as demands grew over time.

 

[MTW]

Do all of these wires connect to just this transformer?


Have you looked end to end for another transformer(s)?

The way it was done in my area, DTE older utility area, the stinger pot is at the other end of the alley, to make up the other leg of the open delta, and run it down the alley in the opposite direction. Forget about the secondary configuration, the three wire primary on top makes it possible. Then there is some 480 pots in between the spread out 240 pots. Open 240 delta services at opposite ends of the block, and some 480 wye service pots in between the open delta ones. Been that way for years.

I have even had them do both service types on the same property for enough load. Just one type to a single building. Multiple buildings on the same property.

 

[kwired]

The way it was done in my area, DTE older utility area, the stinger pot is at the other end of the alley, to make up the other leg of the open delta, and run it down the alley in the opposite direction. Forget about the secondary configuration, the three wire primary on top makes it possible. Then there is some 480 pots in between the spread out 240 pots. Open 240 delta services at opposite ends of the block, and some 480 wye service pots in between the open delta ones. Been that way for years.

I have even had them do both service types on the same property for enough load. Just one type to a single building. Multiple buildings on the same property.

These are possibilities I had in mind for the OP's situation. Seldom or never seen in small towns around here but can see it happening in bigger cities especially in older "downtown areas"

 

[mdlueck]

I made a visit to Saint Joseph, and captured photos of the transformers I remembered.

The other bus, however, is clearly three phase, as that bus is powered by three transformer tubs.

So it seems this four secondary bushing transformer is single phase 120/240v.

Is it the fact that the transformer is rated over 100kw that the casing has heat syncs attached to it?

I would not think split secondary windings vs one winding center tapped would be reason to have the larger tub size with heat syncs.

Do transformers automatically receive split secondary windings when rated over 100kw?

It just looks odd, so I am interested in the engineering reasons why the transformer is wound the way it is.

I am thankful,
Michael Lueck

 

[LarryFine]

Is it the fact that the transformer is rated over 100kw that the casing has heat syncs attached to it?

These are radiator tubes for the oil, not heat sinks in the traditional sense, but they do the same thing.

Having them is one option for any given rating. Having a larger can volume is another.

I would not think split secondary windings vs one winding center tapped would be reason to have the larger tub size with heat syncs.

Nor would I, but most three-bushing transformers are dual windings, not center-tapped.

Do transformers automatically receive split secondary windings when rated over 100kw?

I don't believe so; it's just an older design. Three-bushing units are the same internally.

It just looks odd, so I am interested in the engineering reasons why the transformer is wound the way it is.

Again, it's just an older design of dual-secondary transformers, which most still are.

 

[mdlueck]

Greetings Larry,

Thank you very much!