How is OHLE so robust?

[aleggatta]

When the system trips (and tripping is a very regular occurrence), what happens next depends on the system that controls it, very recent history, and if anyone is working on the kit nearby.

Some systems reclose the breakers automatically, some need manual intervention from the electrical control office. Typically the breakers will be closed twice in succession (ie original trip, close, repeat trip, close) but not a third time. On the third occurrence the power stays off until the section has been inspected.

Historically, the circuit breaker would only be reset twice, as the old standard of oil filled circuit breakers for high voltage were only good for 3 trips before they required servicing to prevent catastrophic failure of the circuit breaker, as a result there would be the initial trip, one attempted reset and one left in the bag for the next trip. With the advent of SF6 filled circuit breakers this is no longer a restriction as long as the circuit breaker has gas in it.

 

[Elecman]

Another reason for limiting trip resets even with Vaccumn and SF6 breakers is to limit the possibility of the wires parting due to the arcing at the point of accidental earthing. It doesnt take many short circuits in the exact same position to weaken and part the tensioned contact wire, especially if it’s a faulty train/ damaged pan that is causing the trip. It is easy to see shorting burns pitting on the contact wire after a pan flash.

 

[Taunton]

On rural overland electricity distribution wires, one of the more common causes of the circuit breakers tripping is lightning strikes, which I presume the OHLE gets as well. Are there lightning conductors bypassing and protecting the breakers at the substation?

 

[a_c_skinner]

Surely the better question is "What's the capacitance of a pigeon?"

I thought capacity and capacitance were synonyms.

 

[richieb1971]

In this video at my home town of Bedford the pantograph seems to clip something, perhaps an unevenly worn cable? In Baldrick terms this causes the "droppers" to fall apart. Is it coincidence that the pantograph clipped the cable at the exact location of points?

 

[The Lad]

Because of the risk of flashovers the catenary wire is solid under tight bridges where the stranded cables would be prone to strands being broken

 

[ole17]

I thought capacity and capacitance were synonyms.

capacitance is more of a physics term, if you didnt know, referring to an ability to store electricity in this case. Everyone has a tiny bit of it, which is how your smartphone's touch screen works when you touch it, incidentally. In the case of the 'pigeon', its 'stored electricity' would (i believe) increase the line voltage to the threshold where circuit breakers might detect a failure and open.

 

[Bald Rick]

On rural overland electricity distribution wires, one of the more common causes of the circuit breakers tripping is lightning strikes, which I presume the OHLE gets as well. Are there lightning conductors bypassing and protecting the breakers at the substation?

It's pretty rare for lightning to strike the OLE. It's known to hit the structures, which of course are earthed.

 

[a_c_skinner]

capacitance is more of a physics term, if you didnt know, referring to an ability to store electricity in this case.

Yes of course and yes I did know, I do think capacity and capacitance are synonyms provided the word capacity is qualified to refer to electrical charge. This seems to put the capacitance of the the human body at 100-200 pFd, effectively zero, so the effect of this for any animal likely to contact the OHLE can be neglected. The current in any arc to earth will be huge compared with that needed to charge the foreign body to 25kV.