Focus on electric locos

In Europe, most of both passenger and freight transport is carried on electrified mainlines. So it's electric locos that are subject to the highest requirements on performance (and operating reliability). And that's why they must be in the focus of the EU drive to enable cross-border operations, too.

For electric locomotives, in addition to separate commissioning, differing signalling equipment, differing loading gauges ( = cross section), and even gauges ( = distance of rails); there is also the issue of differing supply voltage systems. These divide Europe in a hodgepodge pattern.

Sketch of the distribution of electrification systems across Europe (excluding city railways and single branchlines) [own work]

• Yellow: 25 kV, 50 Hz AC (alternating current)
• Red: 15 kV, 16.7 Hz AC
• Purple: 11 kV, 16.7 Hz AC (all of these are metre-gauge)
• Green: 3 kV DC (direct current)
• Blue: 1.5 kV DC
• Light blue: third-rail 750 kV DC
• Grey: only diesel traction or no railways

So, there were plenty of reasons why electric locos for different countries and uses were unique designs – and they made quite a lot of variables to consider when one wanted to standardise those designs. However, the way there was rather non-straightforward. For one, it started with different goals.

The abandoned original idea: universal locomotives

In the seventies, some national railways were thinking: what if the industry could make locomotives that are equally fit for express and stopping passenger trains, and freight? Then, one could realise economies of size in production, less idle time in operation, and less trouble with rare parts in maintenance.

This was the universal locomotive concept. Two advances made it possible technically: asynchronous AC electric motors, and new high-power semiconductors for power electronics. I mentioned this in several diaries before; but here I get a little more technical. Until the seventies, this is how complicated the electric system of a locomotive could get:

1. a transformer reduces the high voltage from the overhead line;
2. a rectifier turns AC into DC for the on-board main circuit;
3. the switch group regulates voltage for the motors (and thus power output) in steps;
4. wound field electric motors drive the wheels through gears.

Some notes:

• Under DC overhead lines, the first two elements could of course be spared.
• Wound field electric motors come in DC and (somewhat less efficient) universal versions; so in many AC locos, the rectifier could be spared, and switching was done on the transformer.
• In diesel-electrics, the input is from a generator (driven by the diesel engine).

While wound field electric engines are efficient in a much wider power-speed range than say diesel engines, and thus don't need to change gears, they still have ideal regimes. So gear ratios were set according to the target top speed, and sizes scaled according to the target power and type of use. Meanwhile, switch groups and the motors (with their friction contacts) were subject to significant wear.

In contrast, the new concept looked like this:

1. transformer
2. rectifier
3. inverter (to turn DC into tri-phase, [regulated] variable frequency AC for the motors)
4. asynchronous AC electric motor (also called induction or squirrel cage motor)

As for the benefits:

• Asynchronous AC electric motors are lighter, yet stronger than wound field ones, and do without friction contacts. Thus, for practical purposes, they have no ideal power-speed regime: they are near 100% efficient from 0 to 230 km/h, from 0 to 1700 kW.

• The engines can be accelerated continuously (no switching between steps) and individually by regulating the output of the inverters. This allows a full use of adhesion, without slips of individual wheelsets. This – in theory – means the need for less axles (four in place of six for heavy freight and 200 km/h express).

• Both inverters and rectifiers use the other innovation: new high-power semiconductors. These are not only smaller and lighter, but enable efficient conversion between DC and AC in both directions. That is, you can brake actively by using the motors as generators, then the inverter as rectifier and the rectifier as inverter, and thus feed electricity back into the overhead line.

The (aborted) development of universal locomotives

From 1971, [West] German Federal Railways DB and makers Henschel (mechanical part) and BBC (electrical part) experimented with inverter-fed asynchronous AC motors in a batch of three test locomotives: the diesel-electric DE2500 (DB class 202).

Above: The look of the ultra-functional design of the seventies... Photo of all three DE2500 by Manfred Richter from the H0 model railroaders of Kusel

Below:The first DE2500, 202 002, on a test run near Waldmichelbach (south of Frankfurt) on a winter day in the early seventies. Photo by Dietrich Seegers from Bahnbilder.de

After the oil crisis hit, in 1974, 202 002 was combined with a driving trailer into one of the strangest animals on rail. What can be best described as a cripple with prosthetics was the ancestor of all modern electrics.

With its diesel engine and generator removed, 202 002 got electricity from the overhead line via a pantograph and transformer installed on the driving trailer. For further tests in the Netherlands, 202 002 was later again rebuilt into a proper electric loco (NS 1600 P).
Photo above by Manfred Richter from the H0 model railroaders of Kusel, photo below by Stefan Motz from rangierdiesel

Finally in 1979, the first application in a high-power mainline electric came: the five prototypes of DB's class 120, the intended proof of concept of a universal loco.

A third, less important technological innovation changed appearance most: turbo fans, with small air intakes on the sloped roof edges, resulted in flat sides.
DB 120 003 opens the 150th Anniversary of Railways in Germany parade in 1985. Photo from Klaus D. Holzborn's Bahn-Internet-Magazin 9

Both the prototypes and the series units (from 1987) proved to be a heavy learning exercise. The new technology and higher power caused a lot of unexpected problems (like fatigue breaks from new types of stresses) that had to be sorted out.

However, just when they finally got the technology working, the German rail industry was caught out cold: the expected giant order for a proper universal locomotive (the still more powerful projected class 121) just never came. For, in the meantime, a spectre started haunting Europe: the spectre of neo-liberalism.

Politics wanted privatisation – and, as a first step, the separation of long-distance passenger, local passenger, and freight operations. Also dividing up locomotives. Good-bye, universal locomotive.

Dumbing down

In the simplest configuration, an electric locomotive's gear creates a rigid connection between motor and wheelset (with cogwheels). Thus the motor's mass rests at least partially on the wheelset, adding to the unsprung mass – the mass interacting with the rail directly.

However, a locomotive's stress impact on the rails (and, in reaction, the strain on the cogwheels) is roughly proportional to both speed and unsprung mass. Meaning, if you don't want to replace track behind (and cogwheels inside) higher speed locos every few years, you somehow have to reduce the unsprung mass.

The way to go was to "remove" the motor from the unsprung mass, by making the motor-wheelset connection elastic. The various solutions all involve a hollow shaft around the wheelset's axle (with the elastic element between that and the axle or the wheel face).

An early example for a hollow-shaft drive: Siemens subsidiary SSW's rubber ring spring drive, made for the DB class E10 (later 110) express loco in the fifties. Back then, the main motivation was not track-related: it was the compensation of the sudden jerks during switches of the power regulator. (Later hollow shaft drives also use f.e. miniature Cardan shafts.)
Scanned drawing and photo from Baureihe110.de adapted with annotations

Now, when the new principle of separated operations arrived, DB's managers thought: the locos of our freight branch won't ever go faster than 140 km/h, so can't we save money if we order ones with simple old axle-hung motors?

Other EU railways followed DB's example. And that's how manufacturers were forced to create dumbed-down versions of the universal locos they just created. Thereby moving towards modularity of production.

You may think, cheaper locos, more orders, everyone wins? Well, not exactly. The choice of 'dumb' motor suspensions for freight locos was exemplary of three ills of neo-liberalism:

1. First of all, railways ditched the service efficiency in using universal locos – an elimination of synergies.

2. Even if the new freight locos are not much worse for the track at 120 km/h than express locos at 200 km/h, the overall mainline track wear is now worse than it would be with universal locos – what's more, worse than before, when even many of the newer freight locos had older hollow-shaft drives. But, for freight operators, track wear is an externality.

3. The locos are cheaper and simpler to maintain. However, wheels and gears suffer higher wear, thus 'age' faster. Not to mention a potential counter-measure against problem 2: higher track access charges. A case of short-termism.

(I discussed these and other vagaries of rail sector 'reform' at length in Globalisation catches up with rail industry?.)

A dead-end

It's not only the supply of asynchronous AC motors you can use high-power semi-conductors for. You can also use them to replace the switch group with continuous regulation in a conventional locomotive. To be specific: thyristors.

In the early years, it wasn't immediately clear that asynchronous AC technology will grow out its teething problems, rather than remain impractical due to excess complexity. Thus, in the seventies and eighties, a number of successful thyristor-regulated locomotives were built.

One family worth to mention (because the current market leader modular family emerged in the same factory) was that of East German maker LEW. After a prototype (1982), they first built 654(!) locos of a slower version (DR class 243, later DB class 143), then 39 in an express version (DR class 212.0, later DB class 112.0, today class 114).

DR 212 001 "White Lady" was the star of the Leipzig Spring Fair in 1982. Next year, it was changed into the slower version to become 243 001. Later, as 143 001, it was a test locomotive for its successive owners AEG, ADtranz and Bombardier. Photo by user Falk2 from Wikimedia Commons

After German Reunification, but before the merger of Deutsche Bundesbahn and Deutsche Reichsbahn into Deutsche Bahn, a remarkable joint order for 90 more in the express version finished the family (class 112.1). Meanwhile, the class 143 became the 'Reunification locomotive': its members were migrated to all regions of former West Germany, too.

The later DR class 243 were equipped for multiple operation, turning them into de-facto universal locomotives on East Germany's slow tracks. After Reunification, they were used for passenger trains.
143 606, in the then current suburban train livery, at the end of a "sandwitched" train on the Ravenna viaduct, on the descent from the Black Forest towards Freiburg, 6 May 1995. Photo by user macpfalz from Bahnbilder.de

In the second part, I will continue to trace the winding route to today's modular locomotives – separately for each of the three main makers.

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