Mains voltage

[JohnW2]

Yes, and pumped through to pressurize them, to maintain insulation and keep out moisture.

I suspect you're thinking of a somewhat different situation. Pumping oil through a hollow conductor obviously would do nothing to 'maintain insulation' (if there were any to maintain).

Kind Regards, John

 

[Harry Bloomfield]

I suspect you're thinking of a somewhat different situation.

I wasn't actually suggesting the reasons were the same.

 

[bernardgreen]

Telecom cables from exchange to street cabinets used to be pressurised, ( air I seem to remember ) to keep moisture out of cables.

AN EXPLANATION OF THE TELEPHONE SYSTEM - MAIN CABLES

AN EXPLANATION OF THE TELEPHONE SYSTEM - MAIN CABLES

www.britishtelephones.com

 

[JohnW2]

I wasn't actually suggesting the reasons were the same.

OK - so what were you suggesting, then?

Kind Regards, John

 

[Harry Bloomfield]

OK - so what were you suggesting, then?

Kind Regards, John

One is the use of flowing oil passing through the cable for cooling purposes. The other is as mentioned by Bernard for Telecoms cables, but I have also seen it used long ago for paper insulated cables, to keep the oil within the power cables, topped up and under some pressure - basically a seal around the cable with a reservoir of oil to keep the cable under a positive pressure.

 

[JohnW2]

Telecom cables from exchange to street cabinets used to be pressurised, ( air I seem to remember ) to keep moisture out of cables.

That was presumable in the cable as a whole, not 'down the centre' of hollow conductors?

In any event, what were the conductors insulated with - presumably something (i.e. not rubber or PVC etc.) that would be adversely affected by moisture?

Kind Regards, John

 

[JohnW2]

One is the use of flowing oil passing through the cable for cooling purposes. The other is ...

Fair enough. The former has some relation to my comment that I thought that hollow cables have been used for power transmission, but I don't think that 'the other' is/are particularly relevant

Kind Regards, John

 

[Harry Bloomfield]

That was presumable in the cable as a whole, not 'down the centre' of hollow conductors?

In any event, what were the conductors insulated with - presumably something (i.e. not rubber or PVC etc.) that would be adversely affected by moisture?

I said "but I have also seen it used long ago for paper insulated cables, to keep the oil within the power cables, topped up and under some pressure -"

 

[JohnW2]

I said "but I have also seen it used long ago for paper insulated cables, to keep the oil within the power cables, topped up and under some pressure -"

I know you did - but the post of mine you are quoting was a reply to bernard's (relating to telecomms cables) which was posted before you added your contribution, not a response to anything you had written

If you pursue this further, I'll probably just let you have the last word, since that's what you seem to want 7

Kind Regards, John

 

[SUNRAY]

I know you did - but the post of mine you are quoting was a reply to bernard's (relating to telecomms cables) which was posted before you added your contribution, not a response to anything you had written

Kind Regards, John

paper but they didn't stop the air when moved over to polyethelene

 

[Harry Bloomfield]

If you pursue this further, I'll probably just let you have the last word, since that's what you seem to want 7

Eh?

 

[JohnW2]

paper but they didn't stop the air when moved over to polyethelene

That would make sense, but Harry seems to be talking about oil, not air - and, of course, none of this has anything to do with my original comment about hollow transmission cables

Kind Regards, John

 

[JohnW2]

Eh?

Kind Regards, John

 

[AdrianUK]

I was always of the opinion that they are usually a ring, like a ring main 13amp socket circuit for many domestic services. Thus a cable fault in one section, leaves the remainder still in operation.

The LV mains aren't rings. A series of (3 phase) radials will exit each 11kV/400V transformer, via local fuses - these fuses are often in the region of 315 - 650A. Houses, streetlights etc etc will be tapped of this radial as it passes. Some LV radials will supply only a single large user (eg. a small factory unit at 400A /3ph). At the end of the cable one of two things will happen : It with either be "pot ended" - a sort-of heatshrink cap that seals the end of the cable, waiting for possible future extension or, if the end is close to the end of another radial (usually from a different transformer) it will be terminated in a 'link box' together with the end of the other cable.

Link boxes are normally operated with the phase links out & the neutral link in (thus joining the neutral/earth of both transformers to aid resilience). In the event of a faulty transformer its possible to remove the fuses at the transformer end & insert the phase links, thus re-supplying that radial from the other transformer.

The 11kV network is usually operated as a ring (in fact this is a 'Ring Main' as opposed to the 32A circuit in the home which is more correctly a 'ring final'). Each transformer on the ring with have a RMU (ring main unit) were the two sides of the ring terminate. The RMU gives the option to supply the transformer from either leg of the ring or to join the legs & power off both. It will often also provide a facility to earth the transformer and/or the 11kV cables. In the event of a fault on the 11kV network the RMUs either side of the fault are operated to switch the faulty section out of the network & continue to operate that circuit as two radials.

 

[Harry Bloomfield]

Link boxes are normally operated with the phase links out & the neutral link in (thus joining the neutral/earth of both transformers to aid resilience). In the event of a faulty transformer its possible to remove the fuses at the transformer end & insert the phase links, thus re-supplying that radial from the other transformer.

Thanks, that would seem to explain how our supply was maintained, even when our supply cable failed.