Could it be a "static balancer", a special transformer that draws power from the higher voltage phases and "pushes" it back into the lower voltage phases, thereby reducing voltage imbalance.

One type of balancer is as below.

PS I have looked at google maps and cannot find this but the 11kV tx is at Elmers close, opposite the Waters Lane entrance, then it is all ABC.

The zig-zag winding secondary makes it a better balance,  than a zero sequence transformer and is less reliant on the magnetic paths being in perfect balance , but a simple 3 limb core will get you a good way just to begin with, and is far easier to describe.


They do both draw current off the highest voltage phase and stuff it back out in the right phase and power split to prop up the other two phases in proportion to their relative depression. (and as an aside to Alan's comment, sometimes it really is better if the other 2 fuses blow at the same time when one phase drops, depends on the sort of load.)



In the Isle of Man diagram, it makes it clearer once you realise the angles of the windings show the core limb they are on, so

the a to a' winding is  wound over the N to b' one, and

the b to b' winding is over the N to c' one and

the c to c' is over the N to a'

the 3 limbs see a magnetisation pattern moved by 60 degrees but still do the 3 phase thing in terms of the total flux.

Thanks Broadgage and Mike. Yes I saw the 11kV transformer. It is quite big. The static balancer seems to have been added as an afterthought as there are redundant ends showing in my photo above.

Z.

there are redundant ends showing in my photo above.

If you mean the ends of the ABCs, I don't think they're redundant, just a feature of the way they make connections to the ABC conductors - i.e. they clamp on an insulation displacing (or insulation piercing?) terminal along the length of the conductor to make the connection to the insulated & sheathed singles they run down the pole, and the ends of the ABCs are just capped off. I guess they could have cut the ends shorter for neatness or maybe deliberately left longer for possible future additions?

   - Andy.

I thought static balancers were a thing of the past obviously there are a few still knocking about. On the way to Wimborne you pa's a group of houses that had some thing like a voltage regulator  attached to the pole it only had LV connections and also a fairly meaty heatsink. It disappeared when they re wired the LV from open wire conductors to ABCs  and added a new HV transformer. Finally I remember going to a place in a little village for a meal in the carpark was a balancer talk about a noisy beast  it made a proper loud buzzing noise. They asked me can you stop it doing that I thought about hitting it but then thought better of it