Bonding and beyond

[opps]

To expand on my earlier comment, my understanding is that the high voltage and large loop area of 25KV OHLE means that induced voltages in fences and similar are a real concern.

But I'm not aware of similar concerns for trains supplied with "low voltage" DC.

Sorry, I now get your point. As far as I know, the tube runs on 660v. I could be wrong though

 

[bernardgreen]

the high voltage and large loop area of 25KV OHLE means that induced voltages in fences and similar are a real concern.

The voltages that are induced in trackside metal are greatly reduced by the use of "booster transformers" and a "return conductor" installed along the track close to the ovehead 25 kV wire. The booster transformers create a current in the return conductor which is approximately the same as the current in the overhead wire but flowing in the opposite direction. The electromagnetic field created by the current in the return conductor cancels out the electromagnetic field created by the current in the overhead wire.

 

[JohnW2]

...... my understanding is that the high voltage and large loop area of 25KV OHLE means that induced voltages in fences and similar are a real concern.

As for 'high voltage', is it not the current in the overhead lines that determines what will be induced in fences etc. (and higher voltages in the overhead cables will mean lower currents) ?

 

[opps]

When I used to wear a cheap "bomber" jacket, I could feel the overhead electromagnetic field pulsing through the coat and along my arm hairs. Stand back 2 or 3 ft from the edge of the platform, and I couldn't feel anything.