The discs are to shed rain and to increase the surface tracking length, to ensure that if the voltage rises to breakdown, the bit that lets go first is the air gap between the metal horns, not the surface or the insulator core, The core up the middle, although the ends have metal hooks, is an insulator, these days usually an epoxy resin fibre composite.

The biggest problem now is that the field gradient along the insulator will be non-uniform and the flash-over voltage will be reduced.

However, 10/11 is not a big deal unless there are other stress factors like salt water spray or conductive dust.

Mike

The discs are to shed rain and to increase the surface tracking length, to ensure that if the voltage rises to breakdown, the bit that lets go first is the air gap between the metal horns, not the surface or the insulator core, The core up the middle, although the ends have metal hooks, is an insulator, these days usually an epoxy resin fibre composite.

The biggest problem now is that the field gradient along the insulator will be non-uniform and the flash-over voltage will be reduced.

However, 10/11 is not a big deal unless there are other stress factors like salt water spray or conductive dust.

Edit Google maps street view is marvellous.

Apologies, these are not solid cored insulators, but the disk and linked type- these look to be glass but the pin and shackle or ball and socket allows the disks to pivot relative to one another by a few degrees, in one or more dierections.

The path throuhg the insulation between the two bits of metal in each disk,  is only some 10s of mm, and although these are probably about 8 inches accross the surface track distance is going to be nearly 3 times that. The cap and pin and the mating surfaces on the glazed ceramic or glass are ribbed, so the cement has something to key into.

- here at both ends of what I think is the same line. At the power station end, there seems to be a longer strings , and corona disks (to shape the field a bit) while at the load end it is simple arc horns.

Mike

An update.

Yesterday I was using a pair of binoculars which were not too easy to keep steady - it was a bit like counting sheep in a field, they do all look the same...

So with there being no rain so far today, another watering exercise and I took a couple of photographs.

www.ancient-mariner.co.uk/public/20230629_175701.jpg  &  www.ancient-mariner.co.uk/public/20230629_175716.jpg

Which prove that I cannot count...

Would appear that the norm here is for 10 discs and that when I reported a missing disc the repair was to hang the remaining nine off a single one. So there are the same number of discs in each string.

The photo with the trees certainly looks like Wood Lane, the power station end is like looking for a needle in a haystack. Yes, the discs appear to be glass.

Clive

I see exactly what you man. It seems that the lowest 9 discs have fallen downwards a little.

In AM's pic showing all 3 arms, it looks like the top line has 11 disks. the mid line once had 11 disks and one has broken leaving a core, and the lower line has 10 disks.

I must say this is an odd failure mode, unless corrosion has swollen the top cap and pushed down and forced the glass to fracture. - and  normally there is a zinc sacrificial collar to avoid that (as if you do not have the zinc present it can give rust problems, as seen in China on their longer DC runs  - that article has some scary photos of failing insulators- but DC is a different class of problems and corrosion is much faster.)

Those insulators have a cross section similar to this- the exact top hook and pin / clevis or ball/socket  arrangements can vary depending if there is a need to allow more flexibility in one direction,

M.

mapj1 said:

In AM's pic showing all 3 arms, it looks like the top line has 11 disks. the mid line once had 11 disks and one has broken leaving a core, and the lower line has 10 disks.

That is another interpretation of the photos.