Sir Nigel Gresley - The L.N.E.R.’s First C.M.E.

But one only had to look at the USA to see where the future lay regarding Diesel technology!
https://en.wikipedia.org/wiki/Diesel_locomotive

 

There is a well evidenced “sparks effect” from electrification, seen even on schemes like Airedale or East Grinstead where there was no noticeable improvement in rolling stock. That does increase revenue. You also need to bear in mind that electrification does also significantly reduce many ongoing costs - see my comments on the Brighton and Portsmouth electrifications.

I hesitate to draw any conclusions in a discussion about the inter war period about what the railway would or wouldn’t do based on the costs and approaches for recent electrifications; the background conditions are simply too different.

You are right that the management of a railway were considering the business case; @monkeymagic is probably right that the LNER were insufficiently imaginative at that time.

The question is whether that was actively poor, or just not as good as might have been.


Sent from my iPhone using Tapatalk

 

Picking up just that bit (and continuing one of several thread drifts); when and why did that change, with 25 kV OHL now being preferred almost everywhere?

 

Because high voltage AC is cheaper than 3rd rail when scaled up because it needs less fixed infrastructure. It’s also capable of handling far higher power demands than DC


Sent from my iPhone using Tapatalk

 

Third rail is appalling, to be frank. I’ve lived on or near it all my life, did a two year long intensive apprenticeship physically maintaining it. I cannot for the life of me understand why the Southern went for third rail. It’s dreadful. Far more dangerous too at lineside.

 

I think you'll find that the DR inherited a large number of narrow gauge lines which were more common abroad than in the UK. The current HSB network (Harz Mountains) is only a fraction of what used to exist within the region where the 2-10-2T Class 99.2 and the 25kV electric line testify to the gradients that encouraged the use of narrow gauge within that region.

 

The LYR had a side contact version where the live rail was encased in wood and the collector fitted in a narrow slot to pick up from the rail. It was in use on the Manchester to Bury line until it was converted to Metrolink in 1991. It seemed to be less badly affected by ice than the normal type

 

Whilst I agree with the danger point, at the time of installation it was seen as a cheap option that was particularly attractive to a cash-strapped operator but there was little knowledge at the time of safety concerns given that staff were responsible for their own safety and companies did little in the way of protection.
The current DaFT accepts this hence it's policy of 25kV overhead going forward but even they appreciate the high cost of conversion as was identified with the changeover of the Hadfield branch from 1500V dc to 25kV ac last century. In that context what system will be used when the Reading - Basingstoke line is electrified - if it ever is.

 

One of those 'yes and no' issues. Certainly ac overhead was in experimental stages (witness the dual catenary 3-phase complexities). One thing which always tickles me was that the same year the Southern sparked up the Brighton line, they sent a congratulatory message to Magnus Volk, marking the 50th anniversary of his eponymous seafront railway!

 

Ignoring the Waterloo and District Line, the SR only had two electric systems on formation:

- 57 miles of LSWR 660V DC 3rd rail
- 24 miles of LBSCR 6.6kV 25Hz AC overhead

In addition, the SECR had plans for a 1500V DC (protected) live rail; and the Government had recommended 1500v DC overhead - a fourth system.

The realistic choice facing the SR was therefore between 660V DC third rail or 6.6kV AC overhead - or using both, which wasn’t as mad as it sounds as there was relatively little interchange between Central and Western suburban systems, but long term would have made electrification on the Eastern section more problematic.

Given the relatively short mileages involved, I don't think that was the overriding reason for choosing the LSWR system. The 3rd rail had the advantage of being relatively easy to lay, and needed no extra space widthways. OTOH, it would inevitably have gaps, so choosing it was tantamount to a decision that traction would be multiple units for passenger trains, but some other form of traction (i.e. steam) for other services. More substations would be needed with the lower voltage, which was extra expense, although the third rail itself was cheaper than overhead.

The overhead would have been more suitable for loco-hauled trains, and wires could be (and indeed were) laid in sidings. OTOH, AC traction motors were in their infancy and the performance at the time was poor, particularly for acceleration. There was a worry over signal sighting and concerns that significant numbers might need to be moved. Many bridges would not have sufficient clearance so would need rebuilding or gaps in the live wire. Even with loco-hauled electric trains, the reality would have been steam over electric routes for years to come, and the overhead was considered more dangerous for loco crew than third rail.

Taken together it was a balanced choice; neither option had overwhelming advantages. My hunch is that the poor performance of AC motors at the time probably swung it, with technical development of the AC system by no means guaranteed at the time.

Tom

 

Good point on clearances and bridges. A lot of them had to be raised and rebuilt when the West Coast main line was electrified at 25kv in the 60s.

 

I seem to recall BR came to the conclusion that the sort of clearances shown by initial calculations (for 25kVac) were a fair bit more generous than actually needed. They also learned the hard way that OHLE operations didin't need the entirety of the steam era track layout. Afraid I'm completely ignorant concerning what level of civil engineering was involved in the LBSC schemes.

Whilst loading gauge clearly was an issue, those on the ex-LBSC section were more generous than most. I've seen an old image of a 4DD unit emerging from the tunnel at Haywards Heath. As these spent their entire lives working Charing Cross/Cannon St to Dartford (via Greenwich, Bexleyheath and Sidcup) this was presumably a gauging test run, before their shortcomings became evident. To the best of my knowledge, their use on Dartford services required little, if any structural work. Indeed, avoiding the costs of such work was why they were built.

The early Alpine and Appenine 3-phase (dual catenary) systems involved substantial sections in tunnels. These necessitated different arrangements, but seems to have worked satisfactorily for some years.

Tom's point concerning control systems may certainly carry some weight, though the ac motors themselves are of simpler construction.

 

Having been on the Jungfraubahn, it’s very obvious why 3 phase overhead didn’t spread.


Sent from my iPad using Tapatalk

 

i think clearance in tunnels had a lot to do with it

 

The LBSCR gauge was notably tall. At 9ft width it was higher (12') than any other pre group gauge (except broad gauge) that I have found. At that mark it was a foot higher than the LSWR or SECR gauges.
Here it is against a current NR gauge.

 

My recollections from my reading are that the LSWR chose third rail for a degree of compatibility with the District Line, because they'd have to share track. I also recall reading that at some point after the Grouping, Raworth compared the maintenance costs of the AC and DC multiple units, and found that the AC ones were about twice as expensive as the DC ones.

 

While I wouldn't like to present myself as any sort of expert in electric traction, as far as I understand it most AC electrics (certainly nearly all those from about the '50s to maybe the '90s in the UK) used DC or 'universal' motors, running in the voltage range from a few hundred volts to maybe 2kV. True AC motors, at least in high power applications, really need a supply of 3-phase AC, preferably with frequency control for speed control, although wound rotor motors did allow for speed control from a constant frequency supply prior to the development of more modern power electronics. Where AC motors are used on modern traction, the incoming supply will be rectified to DC, then some variant of pulse width modulation used in the control to synthesise AC waveforms of the voltage and frequency desired.

For any system using as much as 6.6kV, this presents two problems: First, you need to step down the voltage to something the motor can use (a transformer becomes necessary), you need some way of controlling that voltage, and you probably want a way of turning it into DC (a rectifier). The transformer is the easy bit (if potentially big and heavy), but prior to the rapid development of silicon-based semiconductors (which is post WW2) we're talking about mercury arc rectifiers. These work very well in the right applications, but I suspect are about as fun to deal with as they sound (some of the early BR AC electrics had them, later to be replaced with silicon). The low frequency of European electrification systems (a lot of 16 2/3 Hz systems out there) was to reduce the lossses inherent in the use of series wound DC motors powered directly by AC, thus side-stepping the rectifier issue. To get the low frequency they used AC-AC motor-generator sets in the substations, dividing the mains supply frequency by 3 (hence 16 2/3). But now you need a transformer capable of transmitting the same power at lower frequency, which is going to be bigger and heavier. The voltage control is probably going to be done with a tap-changer on the transformer for either system, basically using more or less of the secondary winding.

DC supplied at a motor-friendly voltage, as per the LSWR system, just requires some combination of series-parallel, field switching, and resistance grids, to give a reasonably granular control, all without having to fit transformers and rectifiers. Especially if you're envisioning the EMU as your main solution, this is a considerable saving in equipment, which is instead concentrated at the substations. For short-distance surburban systems the transmission losses are less significant, and certainly as regards trackside safety the past was another country.

Basically I would argue that the silicon rectifier was probably the key technology for making AC multiple units economically favourable compared to DC, but the Southern was very committed by the time that came around.

 

I am sure I read somewhere, that for later electrification schemes, the catenary could be canted over under tight clearance overhead structures. In this way the electrical field was flattened thereby reducing the chance of arcing. Can anyone confirm?
Certainly the re-electrification of the GE lines out of Liverpool Street were energised at a reduced voltage of 6.25KV (from memory) and Units automatically switching over to 25KV somewhere around Shenfield, presumably because of low overhead structures. The lines were later upgraded to full 25KV and I think this is where the canting of the catenary was mooted! Again not my field so might be wrong.
An article in a BR regional magazine highlighted experiments done, I think on the Clacton/Walton lines, with a movable section of overhead wire, positioned over a steam locomotives exhaust, which could be lowered to ascertain at which point flash over occurred. A dummy human. of correct resistance, was also involved in the trials to indicate potential dangers to loco crew. One can see why it was less than ideal running steam under the wires, particularly for Firemen!

 

Mercury arc rectifiers were good in stationary industrial settings but suspect for traction purposes, getting "sloshed" about, rather reduced their effectiveness and reliability.
They are quite frightening, and fascinating, to see in the flesh.




Believe it or not there are people that collect and operate them for fun!

 

BR identified how they could manage lower clearances, which led to the elimination of the 6.25kV electrifications. Options including insulating paint (Cardiff) and acceptance of limited clearance (Paisley Canal) have also been used to good effect.

More recently, some of the boiling frogs of electrification costs have come from a pan-European standardisation exercise that British regulators failed to seek appropriate continued derogation from.


Sent from my iPad using Tapatalk