OHLE clearances, and 25kv v 1500v dc.

[edwin_m]

Just received November's Modern Railways where Alan Williams is saying the predicted risk of electrocution to passengers from 25kV (from the RSSB risk model) is one in 300 years.

 

[Elecman]

Maybe we should consider overhead third rail at 750V

What would be the point of that? Low power capacity, difficulty in setting protection against fault current as opposed to normal starting current demand, excessive conductor size and power losses (I2R!!)

 

[3141]

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) ?

As I don't use a selfie stick I'm struggling to work out the circumstances in which anyone would use one long enough to put themselves at risk of electrocution under the old 25kv OHLE clearance, but they'd be safe under the new one.

Then how much has implementing the new clearance added to the cost of the GWML electrification scheme? Even if it's foreseeable that some fool might be able to fry themselves by misusing a selfie stick, I doubt that the cost of the new clearance would be justified, especially if you also took account of the higher capital costs of diesel traction and the emissions at the point of use over 35 or more years.

 

[Elecman]

As I don't use a selfie stick I'm struggling to work out the circumstances in which anyone would use one long enough to put themselves at risk of electrocution under the old 25kv OHLE clearance, but they'd be safe under the new one.

Then how much has implementing the new clearance added to the cost of the GWML electrification scheme? Even if it's foreseeable that some fool might be able to fry themselves by misusing a selfie stick, I doubt that the cost of the new clearance would be justified, especially if you also took account of the higher capital costs of diesel traction and the emissions at the point of use over 35 or more years.

Quite, well said

 

[Spartacus]

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.

Ah, but how about another (usually) metallic pole that you hold up in the air, especially during periods when arcing would be easier than the norm? I'm thinking of the umbrella! I can't remember there being a rash of umbrella related electrocutions when half the commuting population used to regularly carry one.

 

[AM9]

Whilst commuting in the '70s, I clearly remember getting unpleasant low-current shocks from a metal umbrella when standing anywhere near the platform edge of a 25kV OLE line in rain.

 

[HSTEd]

What would be the point of that? Low power capacity, difficulty in setting protection against fault current as opposed to normal starting current demand, excessive conductor size and power losses (I2R!!)

Lower power capacity is an irrelevance on large swathes of the network that are not currently programmed for electrification but would still benefit, especially in a world where the railway risks becoming the polluting transportation mode thanks to electric road vehicles.
Excessive conductor size is almost an irrelevance on a railway where the cost of materials (especially aluminium cables) is negligible compared to the total cost of the works to be carried out.
And I2R is made an irrelevance thanks to modern power electronics enabling such close substation spacings (using cooperative rectifiers) that R becomes very very small, and I drops rapidly as you move away from the vehicle.

25kV has been rendered impossibly expensive due to increases in clearance and the like, and currently conventional third rail 750V is out of vogue because it is more dangerous, even though it is still incredibly safe.

 

[theageofthetra]

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

Who imposed these changes?

 

[SpacePhoenix]

Were the changes in clearances required implemented by the UK HSE or whatever the European equivalent of the HSE is called?

 

[Harpers Tate]

Whether or not it's actually the case (and I don't know) it seems timely to blame the EU for the more generous clearances and the attendant huge increase in costs, timescales and consequent reduction in actual progress, including the massive cutbacks in wiring projects recently announced - and probably the stupid timescale that has applied to Rotherham's tiny bit of OHLE.

 

[KingDaveRa]

Whether or not it's actually the case (and I don't know) it seems timely to blame the EU for the more generous clearances and the attendant huge increase in costs, timescales and consequent reduction in actual progress, including the massive cutbacks in wiring projects recently announced - and probably the stupid timescale that has applied to Rotherham's tiny bit of OHLE.

This sounds quite likely to me. It's an easy out for the government (and indirectly Network Rail) from an expensive project. The wheels of government working their magic, as always.

 

[NotATrainspott]

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.

Or, you could use all that electric car technology to allow neutral sections at stations. There's no problem fitting 25kV AC on 99% of a route, and any costs incurred there would be the same for any other electrification type. The problem for the new standards is that OHLE low enough to fit under bridges is now too low for passengers at stations, and it happens that stations are often built where there is a bridge over the railway. Fit batteries to the train and you don't have to do anything special infrastructure-wise whatsoever, other than a longer neutral section. Replacing 25kV AC on open line sections has no benefit whatsoever due to increased power waste; using it only for low-speed sections or for trains accelerating away from stations isn't as bad but then you have to have two separate power supply systems. Mixing together AC and DC is not going to be cheap in any future scheme, as demonstrated by the Rotherham debacle even when it's just going to be DC initially.

 

[najaB]

Were the changes in clearances required implemented by the UK HSE or whatever the European equivalent of the HSE is called?

Neither. The UK had a derrogation which would have allowed us to continue using our own standards, but apparently someone 'forgot' to do the paperwork and it expired.

 

[AM9]

What would be the point of that? Low power capacity, difficulty in setting protection against fault current as opposed to normal starting current demand, excessive conductor size and power losses (I2R!!)

...and incredible EMC issues!

 

[MarkyT]

Or, you could use all that electric car technology to allow neutral sections at stations. There's no problem fitting 25kV AC on 99% of a route, and any costs incurred there would be the same for any other electrification type. The problem for the new standards is that OHLE low enough to fit under bridges is now too low for passengers at stations, and it happens that stations are often built where there is a bridge over the railway. Fit batteries to the train and you don't have to do anything special infrastructure-wise whatsoever, other than a longer neutral section. Replacing 25kV AC on open line sections has no benefit whatsoever due to increased power waste; using it only for low-speed sections or for trains accelerating away from stations isn't as bad but then you have to have two separate power supply systems. Mixing together AC and DC is not going to be cheap in any future scheme, as demonstrated by the Rotherham debacle even when it's just going to be DC initially.

You'd certainly not want to have to rely on pantographs going up and down at every station thus treated so I agree that suggests long neutral sections through the platforms. It would require all trains passing such platforms under power to be battery fitted or to be able to coast through, not just the stopping passenger services, and that could include very high power HS units as well as heavy freight locomotives. If a non battery fitted though train got stopped in the platform area unexpectedly there'd be major disruption with other following traffic stuck behind it. Lower voltage overhead through stations would be complex in the supply equipment side and require all trains to be capable of switching systems automatically. On some routes BR had short 6.6kV AC OHLE sections originally in areas with difficult structure clearances back in the 1960s, but these were all converted to 25kV later on when our legacy reduced clearances became accepted as adequate in such scenarios.

My 3kV DC suggestion earlier (as well as the original 1.5kV suggestion) would be most suitable for existing DC 3rd rail conversions and extensions in the south east rather than as a wholesale alternative to 25kV network wide. In former 3rd rail areas it could offer greater available power capacity with fewer substations (not as good as 25kV clearly but some improvement nontheless). Also it would use the same earthing and traction return current paradigm as the former 3rd rail system, so might be compatible with existing track circuits and signalling equipment.

 

[najaB]

It would require all trains passing such platforms under power to be battery fitted or to be able to coast through, not just the stopping passenger services, and that could include very high power HS units as well as heavy freight locomotives. If a non battery fitted though train got stopped in the platform area unexpectedly there'd be major disruption with other following traffic stuck behind it.

Class 801 / Class 88 'last mile' gensets would avoid that problem.

 

[NotATrainspott]

You'd certainly not want to have to rely on pantographs going up and down at every station thus treated so I agree that suggests long neutral sections through the platforms. It would require all trains passing such platforms under power to be battery fitted or to be able to coast through, not just the stopping passenger services, and that could include very high power HS units as well as heavy freight locomotives. If a non battery fitted though train got stopped in the platform area unexpectedly there'd be major disruption with other following traffic stuck behind it. Lower voltage overhead through stations would be complex in the supply equipment side and require all trains to be capable of switching systems automatically. On some routes BR had short 6.6kV AC OHLE sections originally in areas with difficult structure clearances back in the 1960s, but these were all converted to 25kV later on when our legacy reduced clearances became accepted as adequate in such scenarios.

My 3kV DC suggestion earlier (as well as the original 1.5kV suggestion) would be most suitable for existing DC 3rd rail conversions and extensions in the south east rather than as a wholesale alternative to 25kV network wide. In former 3rd rail areas it could offer greater available power capacity with fewer substations (not as good as 25kV clearly but some improvement nontheless). Also it would use the same earthing and traction return current paradigm as the former 3rd rail system, so might be compatible with existing track circuits and signalling equipment.

The new Stadler sets for Merseyrail are being fitted with batteries for depot shunting work. Fitting a few battery modules to a train is not going to be a particularly challenging task. The 379 IPEMU trial seemed to just involve swapping out the toilet retention tank for a battery pack large enough to run the entire branch line (as in, allowing the train to run properly independently of overhead power). The battery requirement needed to just accelerate away from a neutral section will be much, much smaller. Obviously new trains would have the easiest integration, but I don't think it would be impossible to fit them to existing rolling stock. It's a simpler integration than adding a diesel genset, as you don't have to worry about exhaust routing.

I don't think OHLE DC is a solution for third rail regions. We need to reduce the need to rebuild bridges, as this is the most expensive, least automate-able and most disruptive for communities. A neutral section is a neutral section, so whether the rest of the line uses 25kV AC or 3kV DC wouldn't make a difference to the clearance requirements at bridges. Creating yet another electrification system doesn't really help anyone, while the 25kV+batteries+neutral section technology is really just a minor variation on existing 25kV. Existing investments in 25kV installations, equipment and skills would still be just as useful.

 

[colchesterken]

Did any work take place when the inner sections of GEML were increased from 6.26 to 25 Kv in the 1980s ?
As I remember the insulators may have been changed, But I was not aware of any clearances eased
I think the changes took place near Maryland sub station ( now a block of flats ). There are lots of low structures on the run into Liv St.

 

[HSTEd]

Or, you could use all that electric car technology to allow neutral sections at stations. There's no problem fitting 25kV AC on 99% of a route, and any costs incurred there would be the same for any other electrification type.

The clearances apply to bridges and numerous other locations now remember, it is only the distance from platform requirement that can be obviated by fitting neutral sections to trains, and you would have to likely make the cable nonconducting to ensure that a train with multiple bussed pantographs doesn't accidentally/on-purpose raise two pans and liven the entire neutral section.

The problem for the new standards is that OHLE low enough to fit under bridges is now too low for passengers at stations, and it happens that stations are often built where there is a bridge over the railway. Fit batteries to the train and you don't have to do anything special infrastructure-wise whatsoever, other than a longer neutral section.

Unless railway practice has changed drastically since the ECML scheme, there are a lot of bridges where the new clearances would be violated, and they are not all at stations!

Replacing 25kV AC on open line sections has no benefit whatsoever due to increased power waste;

The increase in power wastage is negligible, power electronics and the crashing price of substations have seen to that.

using it only for low-speed sections or for trains accelerating away from stations isn't as bad but then you have to have two separate power supply systems. Mixing together AC and DC is not going to be cheap in any future scheme, as demonstrated by the Rotherham debacle even when it's just going to be DC initially.

Was there really any need for the line through Rotherham Central to be readied for 25kV conversion?
Even if electrification between Sheffield and Leeds is approved at some stage in the relatively distant future, it is unlikely that Scunthorpe and thel ike will be wired for even longer, at which point the local diesel trains through Central will have to remain diesel operated anyway.

 

[MarkyT]

The new Stadler sets for Merseyrail are being fitted with batteries for depot shunting work. Fitting a few battery modules to a train is not going to be a particularly challenging task. The 379 IPEMU trial seemed to just involve swapping out the toilet retention tank for a battery pack large enough to run the entire branch line (as in, allowing the train to run properly independently of overhead power). The battery requirement needed to just accelerate away from a neutral section will be much, much smaller. Obviously new trains would have the easiest integration, but I don't think it would be impossible to fit them to existing rolling stock. It's a simpler integration than adding a diesel genset, as you don't have to worry about exhaust routing.

I don't think OHLE DC is a solution for third rail regions. We need to reduce the need to rebuild bridges, as this is the most expensive, least automate-able and most disruptive for communities. A neutral section is a neutral section, so whether the rest of the line uses 25kV AC or 3kV DC wouldn't make a difference to the clearance requirements at bridges. Creating yet another electrification system doesn't really help anyone, while the 25kV+batteries+neutral section technology is really just a minor variation on existing 25kV. Existing investments in 25kV installations, equipment and skills would still be just as useful.

The neutral section platform idea could work very well for smaller wayside stations without platform starting signals. Neutral sections provided for other reasons today are deliberately located away from signals and other places trains are liable to stop or be drawing significant power. If the only trains booked to stop at a particular small station equipped with a neutral section are the local passenger trains which could be fitted with a low capacity battery system just for pulling away a few hundred metres, then these could be included at many locations I agree, while allowing expresses and freights to coast through just as they do for existing neutral sections. The bigger problem is at major stations and termini where the urban landscape often means there are more overbridges and tunnels in the environs and they, being more hemmed in by urban development and track and signal layout, are more difficult to solve for modern clearances. Also trains at termini in particular may have long layovers during which doors will be opening and closing, aircon running, all of which will be draining batteries. This suggests to me some kind of self connecting 'shore supply' in these areas. Perhaps 3rd rail has a future after all! In areas with very dense train service it is likely to be very difficult to avoid having platform starter signals or future block markers at platform ends. Much of the Southern is like this hence my suggestion for an overhead replacement for 3rd rail that MIGHT be able to get away with smaller clearances and fewer bridge reconstructions. Small islands of third rail could remain along an otherwise 25kV OHLE route however, as suggested for terminals and major stations. They needn't have their own substation, rather be fed from the higher voltage line, downconverted locally at each site where required.

 

[NotATrainspott]

The clearances apply to bridges and numerous other locations now remember, it is only the distance from platform requirement that can be obviated by fitting neutral sections to trains, and you would have to likely make the cable nonconducting to ensure that a train with multiple bussed pantographs doesn't accidentally/on-purpose raise two pans and liven the entire neutral section.

It's the clearances at stations which cause the most problems. That's where you have the fewest options to provide clearance, and all of them are more expensive and disruptive. In a built up area around a station, it's much harder to add in a temporary bridge or to get rid of it completely. Getting in massive cranes to move pre-fabricated bridge sections in is also that much harder.

Unless railway practice has changed drastically since the ECML scheme, there are a lot of bridges where the new clearances would be violated, and they are not all at stations!

The increase in power wastage is negligible, power electronics and the crashing price of substations have seen to that.

You still have more stuff to install than if you use a 25kV scheme. The only benefit of lower-voltage OHLE is the marginally reduced clearances. It's still just as expensive to install the 'knitting', or possibly even more due to the increased mass of the cables needed to handle higher currents. It's not like your belief that we should just go back to third rail to get electrification ticked off as soon as we can even if it would be a bit crap.

Was there really any need for the line through Rotherham Central to be readied for 25kV conversion?
Even if electrification between Sheffield and Leeds is approved at some stage in the relatively distant future, it is unlikely that Scunthorpe and thel ike will be wired for even longer, at which point the local diesel trains through Central will have to remain diesel operated anyway.

My understanding is that a big part of the cost came from general route upgrades that would have been needed regardless of the electrification standard. Short of doing a Metrolink and actively removing the Central line from the heavy rail network I'm not sure if anything could have been done to avoid that.

The neutral section platform idea could work very well for smaller wayside stations without platform starting signals. Neutral sections provided for other reasons today are deliberately located away from signals and other places trains are liable to stop or be drawing significant power. If the only trains booked to stop at a particular small station equipped with a neutral section are the local passenger trains which could be fitted with a low capacity battery system just for pulling away a few hundred metres, then these could be included at many locations I agree, while allowing expresses and freights to coast through just as they do for existing neutral sections. The bigger problem is at major stations and termini where the urban landscape often means there are more overbridges and tunnels in the environs and they, being more hemmed in by urban development and track and signal layout, are more difficult to solve for modern clearances. Also trains at termini in particular may have long layovers during which doors will be opening and closing, aircon running, all of which will be draining batteries. This suggests to me some kind of self connecting 'shore supply' in these areas. Perhaps 3rd rail has a future after all! In areas with very dense train service it is likely to be very difficult to avoid having platform starter signals or future block markers at platform ends. Much of the Southern is like this hence my suggestion for an overhead replacement for 3rd rail that MIGHT be able to get away with smaller clearances and fewer bridge reconstructions. Small islands of third rail could remain along an otherwise 25kV OHLE route however, as suggested for terminals and major stations. They needn't have their own substation, rather be fed from the higher voltage line, downconverted locally at each site where required.

What I'm saying though is that unlike bi-modes, the long neutral section + battery system could actually feasibly become a standard part of 25kV electrification. Any arbitrary electrified train will have these batteries, since they'll be 1. cheap and 2. useful anyway for shunting and hotel power during supply disruptions. It doesn't really count as a separate electrification system at all. Trains already have to have batteries anyway, so why not take advantage of the massive improvements in energy density so that they may drive the train too? The New Tube for London trains will have these batteries even though clearly the Tube network is already fully electrified.

Most of the big, important stations with long dwell times are already wired up. Even then, I don't think we'll have a problem, as the amount of power required to run basic hotel services isn't really that much compared to traction requirements. Since the system is geared around the availability of 25kV AC for 99% or more of a journey, recharge times are essentially meaningless. As soon as the train reaches a 25kV zone there's enough power available to charge the battery as fast as the chemistry allows. For heat and cold there could be alternative storage systems like fluid reservoirs, with the HVAC intelligently storing and using when required.

 

[AM9]

Did any work take place when the inner sections of GEML were increased from 6.26 to 25 Kv in the 1980s ?
As I remember the insulators may have been changed, But I was not aware of any clearances eased
I think the changes took place near Maryland sub station ( now a block of flats ). There are lots of low structures on the run into Liv St.

I don't remember anything significant in terms of structural work to meet the 'new'* clearance requirements, - just a programme of insulator (and sometimes support hardware) changes. The first time that I realised that we were travelling under 25kV west of the Mountnessing section isolators was one day waiting for the klunk of the ABB west of Harold Wood or the Chadwell Heath breaks. They didn't happen and as there wasn't the flash and buzz that occasionally happened when the balises didn't work, there was an assumption that 25kV was there at last.

* Following tests and associated studies in the '60s, the original 1955? requirement for a 13inch standard clearance was reduced to about 8inches together with equivalent reductions for the reduced clearances in special cases.

 

[edwin_m]

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

Who imposed these changes?

They result directly from the laws of physics, so the person to blame is your deity of choice!

 

[Elecman]

They result directly from the laws of physics, so the person to blame is your deity of choice!

Indeed and the Laws of Physics are pretty Immutable!! Unless someone invents a superconducting bare conductor that's superconducting at ambient temperatures in this country! I2R rules.

 

[Elecman]

Neither. The UK had a derrogation which would have allowed us to continue using our own standards, but apparently someone 'forgot' to do the paperwork and it expired.

Indeed!!

 

[Elecman]

Excessive conductor size is almost an irrelevance
And I2R is made an irrelevance thanks to modern power electronics enabling such close substation spacings (using cooperative rectifiers) that R becomes very very small, and I drops rapidly as you move away from the vehicle..

Larger conductors need larger catenary and metalwork to support them and closer structure spacing.

Power electronics has absolutely zero effect on the value of R since that is inherent to the material and effective conductor cross section, I is constant for a given load and voltage so does not vary with distance between the substation and load (train), except in cases of serious voltage drop due to excessive distance from the supply point.

You would not build expensive substations with thief transformers and rectifiers closer than absolutely necessary and what's the point doing so as you still have to run an 11/33/66 kv feeding cable between them all and the cheapest Feeder cable is Pole mounted Ariel feeders so if your building those then you might just ascwell make it a 25 KV contac system throughout.

As I mentioned earlier what is needed is the derogation to the TSI as was originally offered but "overlooked" by the powers that be.

 

[MarkyT]

As I mentioned earlier what is needed is the derogation to the TSI as was originally offered but "overlooked" by the powers that be.

Probably steered deliberately by some clever "Sir Humphrey" in the Treasury or Department for Roads who probably had a very good idea of the eventual fallout in the hated rail industry ...

 

[HSTEd]

Larger conductors need larger catenary and metalwork to support them and closer structure spacing.

The larger catenary is of little expense, for the same reason that supposedly makes headspans no cheaper than gantries, fitting a marginally larger mast foundation, with a marginally heavier duty upright and a marginally heavier duty gantry is not going to drastically increae the cost.
You still have the same number of operations and will require the same number of crane lifts - since the weight of the masts is not near the limits of capability of a rail, or lorry, mountable crane.
The only real costs is really the extra cost of materials, which are rather small given the historically low price of steel and aluminium.
And 750Vdc systems would require drastically less overhead clearance than a full 25kV catenary settup.
You would provide a ground level (insulated) aluminium busbar that would be bonded to the conductor system at every single support, which will further effective circuit resistance as on average current will only have to travel through the OLE for 25m. (Half a typical ~50m span)

Power electronics has absolutely zero effect on the value of R since that is inherent to the material and effective conductor cross section,

It is also dependant on the length of conductor through which the current must flow, so the improving performance and reducing cost of power electronics allows reduced substation spacing which reduces the value of R by default.

I is constant for a given load and voltage so does not vary with distance between the substation and load (train), except in cases of serious voltage drop due to excessive distance from the supply point.

This is using a traditional one-substation-supports-one-train layout.
If we leverage the availability of very cheap and effective Hall Effect current sensros, and very cheap power electronics, we can scatter our substation capability along the route, to the point that we can use a LV substation drawing from the convenient grid supply (up to about 300-500kW or so) and thus reduce the distance travelled at high currents.
Since losses scale by the square of currents, providing a little capacity close to the train has a disproportionate effect on losses.

You would not build expensive substations with thief transformers and rectifiers closer than absolutely necessary

But substations aren't really very expensive any more, especially if we are build low power, low voltage ones every few hundred metres along the route.
Indeed a modern low voltage substation does not neccesarily require a line frequency transformer at all whilst still providing the required isolation.

and what's the point doing so as you still have to run an 11/33/66 kv feeding cable between them all and the cheapest Feeder cable is Pole mounted Ariel feeders so if your building those then you might just ascwell make it a 25 KV contac system throughout.

.... because a pole mounted 11kV feeder (which would only be required in rural areas as grid supplies are available in developed regions or wherever 11kV feeders happen to cross the route) is orders of magnitude cheaper than a 25kV contact system? To the point that the price of the feeder is honestly negligible.
I have seen reports that put 11kV feeders (which can be 50 feet away, just outside the boundary fence) around £50-100k per kilomere.

As I mentioned earlier what is needed is the derogation to the TSI as was originally offered but "overlooked" by the powers that be.

Which given ORR intransigence is never going to happen.
The safety ratchet only goes one way.

 

[Elecman]

Your next problem being DNOs will not want unbalanced non continuous leads of 300/500kw imposed on there 11 KV networks especially those rural ones furthest away from the primary Feeder as it will cause untold problems for them and their other customers with multiple harmonics and large on off loads imposing voltage regulation issues.

 

[HSTEd]

Your next problem being DNOs will not want unbalanced non continuous leads of 300/500kw imposed on there 11 KV networks especially those rural ones furthest away from the primary Feeder as it will cause untold problems for them and their other customers with multiple harmonics and large on off loads imposing voltage regulation issues.

This is not the 1960s.
Modern large transistor-based power rectification gear can manage power factors of four or even five nines [0.9999/0.99999], modern units infact sink harmonics rather than produce them. [0.95 PF is achievable even without any correction equiopment]
They would probably be the most perfectly balanced load that they could imagine being attached to their system - indeed modern rectifier control systems [yay for powerful and cheap embedded processors/logic controllers] would allow the stations to monitor each phase voltage independently and draw more power from lightly loaded phases, further reducing imbalance introduced into the system by their [the DNO's] other customers.

And given that most electric railways would see traffic increases due to the low marginal cost of more intensive operations, the loads will tend to blur out.

And DNOs provide 11kV feeds to traction substations in various locations today.
The cost of grid reinforcement is almost negligible compared to the cost of a 25kV overhead contact feeder system, complete with brand new feeder stations that have to be built from scratch.