Steam and overhead power lines question

[mswjr]

Hi all, A question please,I have just watched a video on you tube,a preserved steam loco a black 5 a full speed running under overhead power lines,So why dont they arc down to the loco,I would of thought that the wet steam would be a conductor ,can someone tell me.

[Jenny Emily]

Same reason they don't arc when it is misty or chucking it down with rain. Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

[Phil Bullock]

But lets not try that! Hee hee

 

There are risks associated with non steam operations under 25kv OHLE

 

Boiler fittings on some locos too tall ... yellow stripe added on cab side from Sept 1964, operations south of Crewe banned for these locos...

 

Climbing on tenders - must have been banned

 

Class 43 Warships favoured over 42s under OHLE as exhauts off centre and hence not directly under contact wire

 

Steps up to roof on ends of MK1 coaches removed

 

And some locos eg Kings have had to have cab profile changed and boiler fittings reduced in height to run under OHLE in current times

 

Phil

[Davexoc]

25,000 volts sounds alot, but in static/lightening type electricity terms it isn't that much. You will get tracking across insulators that are dirty or where the glaze is breaking down, but that is just a trickle across the surface. Many years ago I used to walk past Willesden and could hear a crackling sound around one ohle post, then on a damp and dark morning I could actually see the arcing.

 

There was a video somewhere though of a steam loco (at Euston I think) that did cause a bit of a flash, but not to the loco, across the insulators.

 

Dave

[Fat Controller]

Same reason they don't arc when it is misty or chucking it down with rain. Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

Steam, like pure water, isn't conductive; it's contaminants that make it conduct electricity. At this time of year, salt off road vehicles can cause track circuits to drop, whilst in Northern France a few years ago, there were outages on both OCS and Grid lines as salt build up (after strong on-shore winds) on insulators became damp with morning dew.

[Dagworth]

 

There was a video somewhere though of a steam loco (at Euston I think) that did cause a bit of a flash, but not to the loco, across the insulators.

 

Dave

Liverpool Street

 

 

Andi

[Clive Mortimore]

Liverpool Street

 

 

Andi

Look what happens when you convert a carriage heating unit into a locomotive :locomotive:

 

 

Steam, like pure water, isn't conductive; it's contaminants that make it conduct electricity. At this time of year, salt off road vehicles can cause track circuits to drop, whilst in Northern France a few years ago, there were outages on both OCS and Grid lines as salt build up (after strong on-shore winds) on insulators became damp with morning dew.

Hi Brian

 

Your theory about steam from a locomotive isn't quite right, to start with the water boiled is not pure, it is full of all sorts of minerals etc as it is normally pumped straight out the ground into the shed water tower. I know  there were some watering softening plants but they did not remove all the impurities. The other thing the exhaust steam is trying to drag the fire that created it out the chimney with it, ash and coal dust is added to the steam. Many photos of steam locomotives show them working hard, most of the exhaust is smoke. This was used to great effect if the crew knew Eric Tracey was lineside with his camera.

 

The water used in power station boilers is as pure as they can get it, mainly to prevent damage to the turbine blades but it does help with the life of the boiler tubes.

 

I don't know the maths behind the static and kinetic clearances so that arcing does not happen in most wet weather conditions and with steam locos running under the wires. Some clever person does and that is why it is safe for trains hauled by steam locos are able to run safely under the wires.

[Trog]

 

 

Hi Brian

 

Your theory about steam from a locomotive isn't quite right, to start with the water boiled is not pure, it is full of all sorts of minerals etc as it is normally pumped straight out the ground into the shed water tower.

 

By the time the boiler water has been boiled turned to steam and then condensed in the exhaust, it will surely have been distilled with any impurities left behind in the boiler.

 

 

A colleague of mine was involved in tests years ago where they lowered a live 25Kv conductor until there was a constant arc between the wire and the funnel of a steam engine. The idea being to check if this sort of short caused any risk to the engine crew, they found there were no ill effects even if you stood with one foot on the platform and one on the footplate. .

[great central]

Same reason they don't arc when it is misty or chucking it down with rain. Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

 

Not sure I'd want to put that to the test if a story I heard a good many years ago has any truth.

 

According to colleagues working on a building site there was a sheet of steel propped up against the side of the cabin they were using.

Apparently the site toilets were a little distance away and one particular individual used to relieve himself against said steel sheet rather than spend part of his lunch break walking to the toilets. Being midsummer it was beginning to get a little 'whiffy'   so they asked him to stop . He did for a few days but then decided he couldn't be bothered walking to the toilets again so they hatched a plan.

The steel sheet was lifted onto a piece of timber to take it clear of the ground (at this point I'll say I've no idea why the steel was there or why they didn't simply move it!) and a hand wound 'Megger' was connected. For those unfamilair a Megger is an insulation testing device capable of delivering 1000V or so but barely any current.

Anyhow lunch time comes around again and 'friend' heads for his usual place before the lunchtime tea drinking session. They let him get well 'started' then the Megger handle was wound like crazy, followed by a scream of pain from outside   and roars of laughter from inside the hut .

It seems they didn't have any more problems

[Steamport Southport]

I seem to remember there was a ban on steam under the wire during the early 1980s. Possibly unofficial.

 

Brought in after one of the loco crews let the locomotive blow off whilst under the wires and damaged them. I think it was in Manchester.

 

 

 

Jason

[Clive Mortimore]

By the time the boiler water has been boiled turned to steam and then condensed in the exhaust, it will surely have been distilled with any impurities left behind in the boiler.

 

 

A colleague of mine was involved in tests years ago where they lowered a live 25Kv conductor until there was a constant arc between the wire and the funnel of a steam engine. The idea being to check if this sort of short caused any risk to the engine crew, they found there were no ill effects even if you stood with one foot on the platform and one on the footplate. .

Hi Trog

 

By the time the steam hits the OLE it has, as I stated, ash and coal dust from the fire included in it. Steam locomotives work because the exhaust steam drags the heat from the fire trough the boiler, and that includes the smoke form the fire being pulled through the tubes and out the chimney. Also impure water when boiled, the steam can still contain some of the impurities.

[caradoc]

IIRC in the 1980s Class 37s with roof-mounted horns (ie the centre headcode locos) were banned from Liverpool St due to OLE clearance issues.

[Edwin_m]

Liverpool Street

 

 

Andi

In that era I think it would have been 6.25kV not even the full 25kV. 

[Dunsignalling]

 

 

And some locos eg Kings have had to have cab profile changed and boiler fittings reduced in height to run under OHLE in current times

 

Phil

OHLE isn't the only reason for that.

 

Modern (mechanised) track maintenance methods, and line-speed requirements result in ballast on most routes being significantly higher than in the old days, reducing structure clearances even on non-electrified lines where Kings might have previously been permitted to run. BR/Railtrack/NR have adjusted permissible dimensions (and the dynamic envelope) to match reality.

 

The Kings were built to the limits of the GWR loading gauge, which was several inches taller than the current standard. Without modification, they would be barred from most, if not all, of today's network.  

 

John

[Ray M]

I remember my brother in law & nephew,

telling me, about the time, they where on Warrington BQ station in the early 80`s.

When a class 85, in the north bay platform. put up its pantograph, in a heavy downfall.

The pantograph then arced to the platform, with quite a large flash.

albeit they where stood  25 yds away, they where pleased they wasn`t at the side of the thing.

[TheSignalEngineer]

In that era I think it would have been 6.25kV not even the full 25kV. 

25KV. The clip was from 2004 i believe.

[Suzie]

25KV. The clip was from 2004 i believe.

It is after construction of the Broadgate complex above the station.

[The Stationmaster]

I seem to remember there was a ban on steam under the wire during the early 1980s. Possibly unofficial.

 

Brought in after one of the loco crews let the locomotive blow off whilst under the wires and damaged them. I think it was in Manchester.

 

 

 

Jason

 

As I understand things the main problem was the dirtying of insulators and breaking down their ability to insulate.  Hence the fact that on some part of the WCML scheme, with plenty of steam running still going on, the insulators were kept wrapped up for as long as possible prior to commissioning and there were also regular possessions for the cleaning of insulators.

 

I'm rather inclined to wonder if something similar might be needed on the GWML with insulators in position and exposed to diesel smoke for a year or more before they are actually needed?

[The Johnster]

Same reason they don't arc when it is misty or chucking it down with rain. Unless the water stream is continuous, the electricity is no better able to travel through it than through air. It's the same principle that if you were to urinate on a live third rail, you would not get  electrocuted up the pee stream because the stream is not a solid arc of pee.

 

Is this the voice of experience, or your opinion of third rail in general?

[The Johnster]

But lets not try that! Hee hee

 

There are risks associated with non steam operations under 25kv OHLE

 

Boiler fittings on some locos too tall ... yellow stripe added on cab side from Sept 1964, operations south of Crewe banned for these locos...

 

Climbing on tenders - must have been banned

 

Class 43 Warships favoured over 42s under OHLE as exhauts off centre and hence not directly under contact wire

 

Steps up to roof on ends of MK1 coaches removed

 

And some locos eg Kings have had to have cab profile changed and boiler fittings reduced in height to run under OHLE in current times

 

Phil

Didn't know about the Warship thing.

[Zomboid]

As I understand things the main problem was the dirtying of insulators and breaking down their ability to insulate. Hence the fact that on some part of the WCML scheme, with plenty of steam running still going on, the insulators were kept wrapped up for as long as possible prior to commissioning and there were also regular possessions for the cleaning of insulators.

 

I'm rather inclined to wonder if something similar might be needed on the GWML with insulators in position and exposed to diesel smoke for a year or more before they are actually needed?

Surely they'd need to regularly clean the insulators at places like Birmingham NS if diesel exhaust was that much of an issue. Not to mention the Paddington to Heathrow bit.

[Titan]

In that era I think it would have been 6.25kV not even the full 25kV. 

 

It has not been 6.25kV for a very long time, was converted to full 25kV throughout before the introduction of class 315 which are 25kV only, so since about 1980.

 

You also have to remember that steam loco's introduce oil for lubrication in to the steam before it gets to the cylinders, so the steam is very far from pure before it even gets as far as being mixed with the products of combustion anyway!

 

Humidity will affect the resistance of the air. In the case of someone peeing on a conductor rail the droplets are large and well spaced (see mythbusters for demonstration) In this case the droplets are tiny, very densely spaced, and the air is as humid as it is possible to be. It is only when the loco slips that the steam is dense enough to cause the flashover. The wire will be installed at minimum height for clearance to the infrastructure, so basically an all round worse case scenario.

[34theletterbetweenB&D]

Hi all, A question please,I have just watched a video on you tube,a preserved steam loco a black 5 a full speed running under overhead power lines,So why dont they arc down to the loco,I would of thought that the wet steam would be a conductor ,can someone tell me.

 Technical bit.

 

Steam is a gas. It's not visible - no more visible than the air that we have all round us, which is also gas - and like most gases not very conductive unless ionised.

 

What you mostly see coming out of a steam loco is water vapour. That's not a gas but small particles of liquid water that have condensed in air. However conductive that water may be due to dissolved combustion products, each particle is surrounded by air which is a good insulator.

 

When next by a steam loco on which the safety valves are releasing, look very closely just above the safety valve top: there is usually a small gap visible beween the safety valve top and the clouds of condensing water vapour. In that gap is steam - and you cannot see it! Steam never reaches any OHLE.

[PhilH]

Here's another one for you...why don't we get electrocuted when overflow from an injector goes directly onto the third rail....

[TheSignalEngineer]

Here's another one for you...why don't we get electrocuted when overflow from an injector goes directly onto the third rail....

Because

1. The wheels are standing on the rails which form the traction current return path to the substation. 
2. You need to provide a path for the traction current to pass through you.

The pigeons at Farringdon happily stood on the wire until it rained. Then they moved along under the bridge and got zapped when their heads got within arcing distance of the steelwork.