• How and why energized conductor is of negative polarity for Monopolar link in DC transmission.
  • And how can water be used as return path?
  • And why negative polarity cause lesser radio interference?

Refer Image given for clear understanding.

Image given is from Power systems engineering book by nagrath and kothari

  • \$\begingroup\$ Why could water not be the return path? \$\endgroup\$ – PlasmaHH Oct 5 '17 at 6:55
  • \$\begingroup\$ How we will palace wire in water? What if there is fault? And asnweer my other query also please. \$\endgroup\$ – Pravin Kumar Oct 5 '17 at 7:13
  • \$\begingroup\$ You place an isolated wire in the water. Do you actually know how many wires are st the bottom of the ocean? They use submarines for repair task. \$\endgroup\$ – Marko Buršič Oct 5 '17 at 7:29
  • \$\begingroup\$ Just drop the cable into water? And water rarely has a fault... \$\endgroup\$ – PlasmaHH Oct 5 '17 at 7:42
  • 1
    \$\begingroup\$ Lesser radio Interference - I think not. \$\endgroup\$ – Andy aka Oct 5 '17 at 10:55

How we will palace wire in water?

Buy a long stainless steel pipe. Insert pipe in earth so that it makes good contact with water in the ground. Done.

There is a problem with using earth as a conductor because the current will displace all kinds of metals and minerals dissolved in the water. This effect might be less of a problem when the earth is the positive lead instead of the negative.

Also see this site where it states: The monopolar link is not much in use nowadays. In my opinion it has serious flaws and that is the reason for this.

I do not see a valid reason why a negative voltage would be better for overhead lines in regard to radio interference. It is also not clear if the book means negative DC, in which case RF interference cannot happen as DC cannot interfere with RF. Or that the book means negative on AC overhead lines which is wrong as well as AC has no negative.

  • \$\begingroup\$ DC is never DC, there is always a little bit of ac due to varying load, which has a bit potential to disturb, but I doubt is a real issue in real life. Corona discharge however is, and this seems to be the main reason for negative polarity in the wire afaik \$\endgroup\$ – PlasmaHH Oct 5 '17 at 7:40
  • 1
    \$\begingroup\$ My doubt is that why effect of positive lead is more than negative lead in dissolving metal and minerals \$\endgroup\$ – Pravin Kumar Oct 5 '17 at 8:00

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