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Topic Title: Ice on third rail
Topic Summary: Picking up power becoming a problem
Created On: 13 February 2010 06:35 PM
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 13 February 2010 06:35 PM
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eswnl

Posts: 144
Joined: 29 November 2008

Is there a way of keeping the temperature of the third rail above 0 degrees C, to stop the ice from forming on the rail in the first place?

I was thinking about heaters in the form of flexible strips being glued to the sides of the third rail. The power supply for the heaters could come from the third rail itself.
And this need not interfere with the running of the train and not require any modification to the pick ups.

see http://www.electronicsweekly.c...-pick-ups-and-sno.html
 21 February 2010 03:00 PM
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broadgage

Posts: 1359
Joined: 07 August 2007

I dont see why it could not be done, though the costs might be too high to make it worthwhile.
Standard types of trace heating tape are normally only designed for 230/240 volt operation. Therefore either a 230/240 supply would have to be provided, at appreciable expense, or heating tape specialy manufactured for 750/850 volts would have to be used.
Trace heating tapes and similar products are normaly intended for heating earthed metalwork, and a product with specialy reinforced insulation would probably be required to heat a conductor rail.

Alternatively, a very large circulating current could be passed through the conductor rail in order to heat it, several thousand amps at a very low voltage being required.
This would introduce substantial complications re additional transformers and cabling/switchgear.

Either option would entail considerable energy useage, and at possibly at times of peak demand.

The ice on conductor rails seldom forms a completly insulating barrier against current collection, but does impair reliable/continous contact.
Some relief may be obtained by fitting extra pick-up shoes to the train in order to increase the chances of a least one shoe making contact.
Trains are equiped to pick up current from either left or right hand side, the conductor rail being installed on whichever side is convienient.
It might be worth installing conductor rail on both sides of the track in especialy problematic locations, since this would double the chances of a good connection.
The cost would be minimal, but it might add to the risks to track workers.
 22 February 2010 03:57 PM
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broadgage

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An easier option might be to use hot water.
It would appear simple to clip semi-flexible plastic water pipe to the side of the conductor rail. To reduce fuel waste the side of the pipe not in contact with the rail should be thermally insulated.

Hot water from a gas or electric boiler could be pumped through the pipe, preferably "out" along one track, and "back" along the other, presuming a twin track route.
The semi flexible blue water pipe is very cheap, as are pumps and domestic size boilers.
Anti freeze in the water would be prudent.
 23 February 2010 02:46 PM
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Paul1966

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Originally posted by: broadgage
Alternatively, a very large circulating current could be passed through the conductor rail in order to heat it


I don't know about today, but I know that at least at one time that method was used by London Underground for the above-ground stretches of track, the de-icing current being applied as necessary during the small hours to keep the rails clear before switching to normal 630V traction current for the first trains of the day.
 23 February 2010 03:05 PM
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eswnl

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Joined: 29 November 2008




I don't know about today, but I know that at least at one time that method was used by London Underground for the above-ground stretches of track, the de-icing current being applied as necessary during the small hours to keep the rails clear before switching to normal 630V traction current for the first trains of the day.


How did this work?
The cables that feed the conductor rails would have to be large enough to handle such a current.
Did they momentarily short the rail to ground?
 23 February 2010 05:57 PM
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Paul1966

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I'm afraid I can't remember the details now, but it was mentioned in a book about LU that I read a good many years ago. I have a vague recollection of a comment about placing a short across the positive and negative conductor rails at the end of the section so that the current could be applied from the other end, but I can't recall any more specifics.
 25 February 2010 12:40 PM
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s470189

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Joined: 21 January 2002

On the London Underground system there are 2 conductor rails neither of which are at earth potential and, in years gone by, they could connect many miles of conductor rails together with a single rectifier feeding at one end and close a breaker at the remote end that caused a short circuit. This caused a large enough current to flow to stop the conductor rails icing up. Although the current was large the equipment rating was not an issue as a train draws several thousand amps and the equipment is rated for this. This system has long since goen out of use for a variety or good reasons.

Network rail employ strip heater in some locations e.g. steep gradients, but I cannot recall if they are powered from the traction supply.

Whilst the pipes filled with hot water would work it is better not to mix water and electricity if possible.
 25 February 2010 02:21 PM
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broadgage

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Whilst I would agree that water and electricity are best kept apart whenenver possible, I dont feel that plastic water pipes attached to conductor rails would be a problem.
The equipment gets wet every time it rains, and any leakage of the hot water should be no worse.
I would anticipate almost the whole installation being in plastic pipe, which of course is non conductive.
The ends of the pipe connected to the boiler, pump, and control valves should be in metal, and reliably earthed to avoid any danger to persons servicing the equipment.
 17 March 2010 03:16 PM
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pcan

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Can't say I've ever encountered it, but the Eltherm El_Rail product at a glance would appear suitable.

Edited: 17 March 2010 at 03:23 PM by pcan
 19 March 2010 04:10 PM
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obrennan

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Joined: 01 January 2005

The last reminisce of the LUL conductor rail short-circuiting system was removed in early 2008. It was tried at a number of locations (mainly on the Metropolitan Line). As the earlier poster correctly pointed out, the lengths of conductor rail short-circuited were in the order of several kilometres so the short circuit currents didn't exceed the direct acting settings on the DC brakers (often in the region 5000 Amps to 7000 Amps) on LUL. It had not been used since the mid to 1970's as far as we could gather. The equipment removed in 2008 was installed in 1962.

It typically operated by means of a remote breaker in a track side hut at a remote location on the line. The short circuit was instigated by a novel means of a step up transformer (230V to 600 V ac) which was supplied from the sub-station LV ac auxiliary board. The 600 V ac supply was then run track side for the several kilometres to the trackside hut (presumably because running it at 230 V single phase at that voltage was not feasible) to energise the closing coil on the short-circuiting breaker. I never managed to get a definitve answer as to why a DC feed was not used to energise the breaker from the sub-station.

Today, de-icing of the third rail on both LUL and NR is achieved by use of de-icing fluid (Propylene Glycol or other anti-freeze) dispensed from suitably equipped stock passenger stock.
 20 March 2010 11:17 AM
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Paul1966

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Interesting - Thanks for the description. Maybe a separate 600V transformer was used for the remote breakers just to keep those control circuits completely isolated? If the 630V D.C. traction supply were used it would be miles of extra control wiring which could, potentially, introduce an earth fault.
 23 March 2010 09:20 AM
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tpg500

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Network Rail have heating systems in place all over the country to stop ice forming around points (which would stop them moving and could cause a derailment). Most of the old gas heaters have now been replaced with electric heaters.

These points heating systems are 110V strip heaters (about 5m long)clipped driectly to the side of the rail which are generally supplied from a dedicated 400/230V DNO supply and then each transformed down to 110V by individual transformers at each point end. The control gear for them uses hot and cold probes (keeping the temperature in-range like a thermostat) and a precipitation sensor. This makes it reasonably efficient as it's only used when conditions require it (and the whole system is often switched off over the summer months).

A similar system could be used for the third rail, but this would be quite a cost to install and run as there has got to be considerably more miles of third rail than there are points.

I guess it's another reason that third rail traction power is only found in the south of the country, with overhead line being the preferred method in the colder regions.
 23 March 2010 04:39 PM
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eswnl

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Joined: 29 November 2008

Originally posted by: tpg500

I guess it's another reason that third rail traction power is only found in the south of the country, with overhead line being the preferred method in the colder regions.


I think its more to do with history. Using third rail was proposed by the LSWR(london south western railway) and its use quickly spread onto other lines coming out of London. It could also be a direct derivation of London Undergrounds 4 rail system(without the 4th rail), which was electrified years before.
 29 March 2010 09:17 PM
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eswnl

Posts: 144
Joined: 29 November 2008

Another idea.

I was thinking about microwaves and water. Can you feed microwaves into the third rail which allow the third rail to act as a microwave radiator. With the ice being in direct contact with the rail, it would cause the ice to melt.
 03 April 2010 10:58 PM
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z315870

Posts: 65
Joined: 30 May 2003

Third rails are a bit long to be efficient microwave radiators! A *very basic* antenna would be half the wavelength you want to transmit. For microwaves, we're talking a matter of centimetres. However, running a diesel train with some microwave transmitters mounted over where the third rail runs might be one option, as a kind of "clearing-the-way" sort of operation.

There has been a notion of using specially machined abrasive conductor shoes to scrape off the ice, but I'm not sure whether it has been taken up commercially.

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