DART floating?

Dubh Geannain

Hey. Can anyone tell me whether the DART is a floating or a grounded system?

Many thanks

pljudge321

Floating I would imagine, I'll double check for you tomorrow.

DublinDilbert

Well the metal rail's are the 0V reference in the DC system. The rails are bolted to every sleeper along the way, so are in effect have a small connection to ground at every sleeper. Hence i would say its not a floating system!

If it was a floating system you'd be able to touch the 1500V DC wire above and nothing would happen to you. I wouldn't recommend doing this! :rolleyes:

Dubh Geannain

I know that in the past old electrified rail systems grounded the tracks to avoid a shock hazard.

Floating is the preferred choice these days as overvoltage protection techniques can prevent the rails reaching a dangerous level. One of the advantages of a floating system is stray current reduction.

The rails are bolted to every sleeper along the way, so are in effect have a small connection to ground at every sleeper. Hence i would say its not a floating system!

I was thinking about this too. Is there any insulation or are they just a bolt into the sleeper.

Edit: Thanks pljudge. I'd like to know definitively.

pljudge321

I should have you that answer for you tomorrow.

The dart line uses insulated clips to hold the rail in place. These clips connect to a baseplate which are bolted to the sleepers so the actual rail is insulated from ground as far a I know, I am open to correction though.

Dubh Geannain

Sounds like floating to me, which I'd expect. Thanks.

DublinDilbert

If it is floating what stops people getting a small shock from the rail? Are they clamping the 1500v WRT ground? Surely there would be some small touch voltage on the rails...

pljudge321

Turns out that its grounded after all.

DublinDilbert

Out of interest what would be the advantage of having such a system floating??

Just in case i'm ever asked to design a rail way

Dubh Geannain

Thanks for that. I'm quite surprised tbh.

If it is floating what stops people getting a small shock from the rail? Are they clamping the 1500v WRT ground? Surely there would be some small touch voltage on the rails...

With a floating system the current return path i.e. the rails are insultated wrt to ground. Floating systems have the hazard of the rails drifting to a dangerous voltage. This is catered for by implementing overvoltage protection techniques like an arrester or something similar which short the rails to ground should a momentary high voltage be attained by the tracks for whatever reason.

That's my understanding anyway.

Dubh Geannain

DublinDilbert wrote: »

Out of interest what would be the advantage of having such a system floating??

Just in case i'm ever asked to design a rail way

One of the advantages is stray current reduction. Causes unseen damage to underground metal work.

http://corrosion-doctors.org/StrayCurrent/Transit-Systems.htm

DublinDilbert

Dubh Geannain wrote: »

One of the advantages is stray current reduction. Causes unseen damage to underground metal work.

http://corrosion-doctors.org/StrayCurrent/Transit-Systems.htm

I seem to remember something about the Luas rails and grounding alight, I'm wondering is this a floating system? Probably more of an issue for the luas considering it was pretty much a new route through the city etc...

Dubh Geannain

The Luas a floating system. Although it wouldn't appear to be if you think about the embedded tracks. They may be embedded but they are insulated.

Of course it's impossible to isolate it entirely from ground as there is an almost infinite amount of possible paths in parallel.

I think it actually requires more current than the DART due to it operating at a lower voltage 750VDC (DART is 1.5kV) hence the increased stray current risk and the need for a floating system.