OHLE clearances, and 25kv v 1500v dc.

[Kneedown]

Been mulling this over for a while and thought I would open it up for opinion.

It is apparent that one of the factors contributing to the increasing cost of electrifying lines, and the curtailment of some schemes, is due to increased clearance standards for the OHLE equipment, resulting in bridges having to be raised higher, vegetation and other structures moved further away etc.
On routes where clearance is an issue but which would otherwise justify electrification, would it be prudent to return to the 1500v dc system which requires less clearance?
Of course, more feeder stations would be required, and heavier wire used which would be an expense, but could it be more cost effective than the additional clearance work required for 25kv?

 

[Elecman]

What is needed is the sensible descision that the originally used clearance values ( perfectly safe for 50+ years) to be reinstated as the offered derogation to the TSI would have permitted

 

[Elecman]

1500 volt dc would require much more intrafstructure substations/rectifiers and much heavier conductor wires and catenary to take the much higher currents, also needing some form of multi voltage capable traction

 

[MarkyT]

... would it be prudent to return to the 1500v dc system which requires less clearance? Of course, more feeder stations would be required, and heavier wire used which would be an expense, but could it be more cost effective than the additional clearance work required for 25kv?

Perhaps a higher voltage of 3kV DC might also be possible with reduced clearances, as used in Belgium and parts of Eastern Europe. That could reduce current and the number of substations compared to 1.5kV.

 

[ijmad]

I've always thought a better solution would be on-board battery packs to bridge between electrified sections, with a way to automatically lower the pantograph to get under low clearance bridges and tunnels at speed. We're not far away from this with some of the technology on the 800s.

 

[Harpers Tate]

I'm with post #2. It was demonstrably safe (by which I mean, there have been no problems, incidents, issues, etc) when done to the "old" standards, so we do not need a new, more costly standard. That is nothing more or less than a waste of money, without any demonstrable benefit.

 

[ilkestonian]

If a different system were required, what is wrong with the solution which was implemented fifty years ago, when the WCML electrification was done?

6.25kV in areas of restricted clearance, with (I believe) automatic changeover from 25kV to 6.25kV and vice versa.

The fact that the 6.25kV was changed to 25kV after a while rather proves the point that no change is now necessary though...

 

[furnessvale]

Been mulling this over for a while and thought I would open it up for opinion.

It is apparent that one of the factors contributing to the increasing cost of electrifying lines, and the curtailment of some schemes, is due to increased clearance standards for the OHLE equipment, resulting in bridges having to be raised higher, vegetation and other structures moved further away etc.
On routes where clearance is an issue but which would otherwise justify electrification, would it be prudent to return to the 1500v dc system which requires less clearance?
Of course, more feeder stations would be required, and heavier wire used which would be an expense, but could it be more cost effective than the additional clearance work required for 25kv?

Without digging out my blue book, I seem to recall that 1500dc, because it is dc, actually requires MORE clearance than 25kvAC.
3000dc suggested elsewhere, would be even worse.

 

[GRALISTAIR]

I'm with post #2. It was demonstrably safe (by which I mean, there have been no problems, incidents, issues, etc) when done to the "old" standards, so we do not need a new, more costly standard. That is nothing more or less than a waste of money, without any demonstrable benefit.

Yep exactly

 

[Kneedown]

Without digging out my blue book, I seem to recall that 1500dc, because it is dc, actually requires MORE clearance than 25kvAC.
3000dc suggested elsewhere, would be even worse.

Pretty sure that an RSSB publication (I forget which) says otherwise.
I'm not an electrical engineer and so will bow to greater knowledge, but I was going on the minimum safe distances which are 9ft for 25kv ac, and for dc.... well just make sure you don't touch it.

 

[furnessvale]

Pretty sure that an RSSB publication (I forget which) says otherwise.
I'm not an electrical engineer and so will bow to greater knowledge, but I was going on the minimum safe distances which are 9ft for 25kv ac, and for dc.... well just make sure you don't touch it.

I'll try and find my blue book tomorrow. This book gives the actual minimum clearances required from wire to structures and loading gauge, as opposed to the "keep clear of" figures which are extremely generous for personal safety reasons.

 

[Bald Rick]

75mm min clearance for 25kvAC. Plenty of places where that is done without issue. Unless a pigeon gets in the way.

 

[Ships]

75mm min clearance for 25kvAC. Plenty of places where that is done without issue. Unless a pigeon gets in the way.

Or a selfie stick/metallic balloon

 

[CyrusWuff]

Found a copy of the Blue Book on the Railways Archive.

The recommended structure clearance above rail level for speeds of up to 200km/h (125mph) is given as 4640mm (approx. 15'3) for 25kV AC, though the preferred clearance is 4780mm (15'8); and 4440mm (14'7) for 500-1500V DC and 6.25kV AC, though again the preferred clearance is higher at 4580mm (15').

At level crossings, these increase to 5600mm (approx. 18'4) for 25kV AC and 5500mm (approx. 18') for 500-1500V DC and 6.25kV AC.

 

[D365]

Or a selfie stick/metallic balloon

Can you point me to any incidents so far where either of those items have come into contact with an overhead catenary?

 

[najaB]

Can you point me to any incidents so far where either of those items have come into contact with an overhead catenary?

"It's never happened so it's safe." isn't the approach real H&S professionals take.

 

[SpacePhoenix]

Found a copy of the Blue Book on the Railways Archive.

The recommended structure clearance above rail level for speeds of up to 200km/h (125mph) is given as 4640mm (approx. 15'3) for 25kV AC, though the preferred clearance is 4780mm (15'8); .

Does it go up by much for speeds over 125mph?

 

[NSEFAN]

"It's never happened so it's safe." isn't the approach real H&S professionals take.

There has to be some consideration of risk and the consequences. The consequences of a human connecting 25kV AC to ground are inherently fatal in all cases, so in order to use this power system we have to find a compromise. A determined passenger can still climb on top of a train and zap themselves, even with larger clearances. If there's no significant rise in safety incidents involving the public and OHLE then surely that's an indication that the risk is low enough to keep using the existing standards?

 

[najaB]

If there's no significant rise in safety incidents involving the public and OHLE then surely that's an indication that the risk is low enough to keep using the existing standards?

I don't disagree, I'm just pointing out that 'It's never happened before.' isn't the same thing as 'It will never happen.'

25kV electrification has been around in the UK for the better part of 60 years, selfie sticks have been around for about 5.

 

[QueensCurve]

On routes where clearance is an issue but which would otherwise justify electrification, would it be prudent to return to the 1500v dc system which requires less clearance?
Of course, more feeder stations would be required, and heavier wire used which would be an expense, but could it be more cost effective than the additional clearance work required for 25kv?

Not just more feeder stations and thicker wire. A much higher current is needed to deliver the same power. This in tern means much higher transmission losses.

500V DC is used on the Tyne and weir metro but even they are looking at going to 25kV. One issue is that the fault protection cannot discriminate between a fault and the current drawn normally by trains. This has caused problems on 2 recent occasions.

 

[D365]

"It's never happened so it's safe." isn't the approach real H&S professionals take.

I'm not sure why you are jumping to that conclusion.

 

[QueensCurve]

I'm not sure why you are jumping to that conclusion.

You have to protect against all "reasonably foreseeable" hazards, not just those that have presented previously.

 

[edwin_m]

You have to protect against all "reasonably foreseeable" hazards, not just those that have presented previously.

Indeed, but 25kV has been in operation over a wide area for several decades, which should give enough data to establish with reasonable confidence how frequent different accident types are. You also don't have to eliminate hazards completely, just ensure the risk is not at an intolerable level and has been reduced as low as reasonably practicable. "Reasonably practicable" does allow you to say that it would be impractical or too expensive to introduce a particular mitigating measure.

 

[NSEFAN]

I don't disagree, I'm just pointing out that 'It's never happened before.' isn't the same thing as 'It will never happen.'

25kV electrification has been around in the UK for the better part of 60 years, selfie sticks have been around for about 5.

Would selfie sticks pose more of a threat than helium party balloons (which have been around for longer and can easily reach much higher than a selfie stick and blow around to make accidental contact with OHLE equipment) ?

 

[QueensCurve]

Indeed, but 25kV has been in operation over a wide area for several decades, which should give enough data to establish with reasonable confidence how frequent different accident types are. You also don't have to eliminate hazards completely, just ensure the risk is not at an intolerable level and has been reduced as low as reasonably practicable. "Reasonably practicable" does allow you to say that it would be impractical or too expensive to introduce a particular mitigating measure.

I don't disagree with any of that. It is just that you do, if something new is identified, have to consider the hazards. Not just "Reasonably Practicable" risk reduction. "Reasonably Foreseeable" hazard identification too.

 

[HSTEd]

There was research in the Soviet Union on 6kV and even 12kVdc systems, since they tend to be more forgiving to weaker power grids than 25kV Ac installations, which inevitably impose horrible grid imbalances on the supporting system. After all an AC railway locomotive (on 25kV atleast) is an inherently single phase load, rather than the desirable three phase.

With advances in rectifier technology it is highly likely that 1500Vdc would be perfectly viable (the same stuff I mention for 750Vdc, but modified for 1.5kV instead), but Network Rail simply doesn't want electrification if it can't have 25kV.
It would rather keep the diesel railway until electric cars make it politically impossible to support keeping it open.

75mm min clearance for 25kvAC. Plenty of places where that is done without issue. Unless a pigeon gets in the way.

Good luck ever getting permission to do that ever again.

This document [page 43/82] from the HM Railway Inspectorate indicates that the NORMAL MINIMUM 150mm static clearances are required for 1500V, with passing clearances as low as 100mm.

As opposed to the 300mm+ now required for 25kV.
It also notes that at these voltages, especially at 750V nominal, can potentially be reduced and that physical considerations rather than arc considerations dominate clearances.

Maybe we should consider overhead third rail at 750V

 

[misterredmist]

The 'new' 25kv clearance regs are just a load of bureaucratic poppycock created by H&S gone mad people to keep themselves busy and justify their positions, inflated salaries and pensions...... The world has gone mad..... what happened to the old adage of 'if it ain't broken, don't fix it' ? No doubt there'll be some more nonsense coming 'down the line' on some other issue in the next few years.

 

[LNW-GW Joint]

Picture taken out of the back of my Naples-Catania train last week, somewhere south of Paola.
The 3kV DC OHLE compares very well with our classic 25kV system, though the knitting does seem more complicated (eg double contact wire).
But the lineside lattice masts look pretty good to me, rather like the 1960s WCML design.
Like most Italian main lines, it's a 160km/h route.
3kV DC also applies on the 50km new high-speed LMV line (Linea Monte Vesuvio) between Naples and Salerno, which is a 250km/h route.

 

[Bald Rick]

Incidentally there are plenty of examples of metallic helium balloons coming into contact with there was one near Mill Hill a couple of weeks ago. Fortunately not any that I know of where someone was still on the other end.

 

[D365]

Maybe we should consider overhead third rail at 750V

Safety isn't the only reason why we have not pushed for any further implementation of third rail.