ECN Forum Forums Photo Discussion Forums Photos for General Discussion Primaries of pole mounted transformers

I was in Tampa for a few days up north of town in the lake area. They have single primaries on the poles and wire L/N there too. Must be an FPL thing

Very interesting!

Square-ish aerial transformers seem to be common in many countries outside the US. Virtually all of ours are cylindrical, at least since the 1940s.

In the 1960s GE introduced the "SealPak" transformer which had a shape somewhat like the one in your picture, but I don't think they caught on; at least I've never seen one except in ads.

Do aerial transformers in the UK typically have primary fusing or cutouts? In the photo, it appears that the primary leads are connected to the lines by hot-line clamps, which would serve as disconnects.

They've certainly been the norm here for a very long time. Here is another single-phase xfmr, this time feeding 3-wire 240/480V local distribution lines in a rural area where there are a few dozen homes scattered along a backlane (primary is 11kV again):



The typical 3-phase xfmr looks very similar, although obviously with 3 HV bushings and 4 LV terminals.

We've started seeing one or two new types in the last few years though, like this cylindrical unit which is much more North-American-looking:



Or this one, which at first sight seems odd for having the HV bushings vertical instead of at an angle like almost all of our older xfmrs:





There's not usually any fusing on overhead xfmr connections here. Cut-outs and sectionalizers can be found in some places.

I've seen a few rectangular air-cooled pole-mounted transformers in my area (VA, USA). I'll take a photo if I get a chance.

Actually we have quite a few square and rectangular pole mounted single phase transformers around my area as well, but they are older. I would guess some are from the 50's and 60's era when the cases were painted black or green but I have seen a few painted grey which seemed the norm around the 70's, unless of course they were "rebuilts".
All 3-phase transformers remain rectangular, and I will try to get pix as well in the next few days as well.

A.D

Same around here, the original transformers here from the 50s were/all are rectangular. So are the three phase transformers, but Peco doesn't hang many of those around here anymore, instead using three separate transformers.

Ian A.

I don't think I've ever seen a US pole mounted three phase transformer before in real life. (Post those pics guys )
I remember seeing a photo in an old book of a pole mounted transformer: it had four secondary bushings and four wires extending down to feed the secondary rack. There where both four wire and three wire service drops extending from the secondary rack. I thought immediately that it was a three phase pole mounted transformer. The weird thing was that I could only see two primary bushings (the side mounted kind) and two primary wires extending down from the primary crossarm and cutouts. How could that work? I have observed that modern single phase (and single primary bushing) transformers that are connected phase to neutral have the primary grounded neutral conductor tied to the center tap of the secondary. (essentially the primary and secondary neutrals are the same wire) But I didn't think that the three phase transformer in the old photo would be wired this way. (It looked to be connected the same way as a single phase transformer would be to a delta primary)

Any Ideas?

(digging deep in my memory, I believe the book was on appliance repair, early sixties vintage, and it had a few pages on how electricity is delivered to homes)

The only time I saw a pole-mounted 3ph was in New Hampshire. There, they also seem to put much larger transformers on poles than I would think to (200KVA+) and have been using the insulated primary system with the plastic hangers for a while now. In fact, I think the wire and hangers were invented and manufactured in New Hampshire. IIRC, it had three primary bushings and four secondary lugs.

Never seen a pole-mounted square transformer in use, but there is a PUD on the coast here in Oregon that uses what appear to be clear-coated stainless steel transformers (on the topic of nonstandard pole pigs). None of them seem to be rusting, and all are shiny which suggests that they didn't just have the paint peel off. They look interesting, since pretty much everywhere else has the same old gray ones.

Interesting the differences between the UK and NZ.
We use in NZ the two phase supply or the SWER (single wire earth return) system. (washing line)

In the second case the 11 or 6.6 kV single wire is taken off an 11/11 or 11/6.6 kV isolating TX to avoid having the feeder trip on earth fault. The secondary voltage is 230/460 or 240/480 Volts.

But on the first photo of this thread, it looks like a SWER system set up.

Sounds like it might have been an open delta with one primary leg grounded. Either either that, or the other bushings were just hidden from view.