Pylon insulator replacement

[ross94]

Hi all got an interesting question here, I've noticed the high 275kv voltage pylons around my area are having their insulators replaced. I noticed the men hanging on to the tower attached to ropes while swapping the insulators. Very interesting to watch.But how do they do it without bursting into flames? surely they cannot do that live! it needs to be turned off but how? I image if they just turn it off then a good part of the town will lose power. Do they perhaps go to the each hv substation where the pylon runs and at both ends sort of jumper link that hv circuit which the run they are working on originally supplies from another live hv circuit to maintain the power and then disconnect the run at each end from both HV substations?

sorry if it doesn't make much sense. They were only changing one side of the pylon so I would guess the other side was live. cheers

 

[sonicm1etn]

one half is 'live' you will see red flags indicating the live side. They can turn them off on the side they are working, as the power is rerouted via another transmission section

 

[Nozzle]

Each side of a pylon (transmission tower) is a separate circuit - which may (but it doesn't have to) terminate at the same substation/mesh. So three phases on one side can be isolated first by opening a breaker - then a disconnector, then applying an earth. Later, if the cable are to be dropped for a replacement they'll be anchored to the ground too - as much to keep tension (and thus balance) but for electrical grounding too.

Nozzle

 

[SimonH2]

No they won't be doing it live - the circuit will be switched off and earthed. At that level, there is a fair bit of flexibility and redundancy in the network which is partly to allow for this sort of work.
Traditionally, there has been as much as 100% redundancy, but these days there is a big push on to "make better use" of the assets and so the level of redundancy is being reduced. But in addition to having redundancy in power routing, they can also bring in portable generators to supplement supplies where there isn't sufficient redundancy.
I happen to know that where my employer's office is, we are fed from a substation on the end of a pair of 132kV circuits (which are actually a branch tee'd off a main circuit). At the other side of town is a single 132kV circuit into another substation. And there is a 132kV underground connection between them. A few years ago we had a power cut when storms hit, the neutral wire broke and dropped onto the phase wires on the main circuit. With both main feeds off, they didn't have enough power to get our substation going again without getting the factory up the road to run off their own generator.
They were able to drop some link cables off at the junction and disconnect the main circuit, allowing them to restore full power. Given the weather at the time, I hope the linemen involved in the work got a thanks from their management !

 

[Lectrician]

Neutral?