(07-27-2017, 01:54 PM)trainspotter139 Wrote:(07-26-2017, 06:41 PM)Canard Wrote: So if the polarity of the contact wire and rails were reversed, it wouldn't work? I'm assuming the contact wire is negativley charged then, since electricity flows from - to +, right?
If polarity were reversed a flood would short the circuit and the TPSS breakers would trip. In the case of normal polarity a flood would still allow the ground return to operate in the same fashion.
Nope. With the -ve of the DC source in the TPSS tied to the tracks/ground and +ve to the contact wire, a flood is harmless. If however the +ve of the DC source in the TPSS were tied to the tracks/ground and -ve to the contact wire, a flood would still be harmless because the track and ground remain at the same potential, which just happens to be +ve compared to the contact wire.
The phone companies (and the telegraph companies before them) have done it the second way since forever, because that way everything is either negative (tip) or slightly negative (ring) compared to ground, which prevented galvanic corrosion of the copper wires. I was surprised to read Schedule 15-2 Article 6 of the project documents and discover that it wasn't being done that way for transit. I'm sure there's a reason, I just don't know what it is.
...K