20 years ago, and 2 years after the East Coast Main Line (ECML) was electrified from London to Edinburgh – only 10 years late – BR’s flagship locomotive “Electra”; also known as Class 91, saw service for the first time on the West Coast Main Line (WCML). To be fair it didn’t last long on the WCML, but in 1992, it set a fastest service record, with a train from London Euston to Manchester Piccadilly in 2hrs 8mins. At the time this loco was being developed, British Rail – and the InterCity Sector especially was making significant operating profits – and the completion, finally of the electrification work on the ECML was perhaps the icing on the cake.
The profitability of British Rail continued into the early 1990s, and in 1992/3, this press release was issued alongside the annual report:
In 1991, they put out this publicity brochure, to advertise what was coming:
Please click on the image opposite to read on >>
The “Electra” Project – the Class 91 – was one of the most innovative locomotives then developed for use on British Rail. In its Bo-Bo wheel arrangement it was able to generate some 4.54MW of power and haul 11-coach rakes of the new Mark IV coach when it became available. On the WCML it was planned to haul 750 tonne sleeper trains single handed, and the West Coast route, with the arduous ascents of Shap and Beattock between London and Glasgow, was much more demanding than the East Coast.
Thirty one Class 91 ‘Electra’ locomotives were ordered by BR, along with 50 of the Class 90 (formerly known as 87/2), and 86 sets of power equipment for the Class 319 multiple units. The locomotives featured the latest thyristor control systems, with more extensive use of microprocessors, and in a radical departure the separately excited (sep-ex), d.c. traction motors were included in the bogie space, but carried in the locomotive body.
The electrical equipment included oil cooled traction converters – featuring GTO thyristor components – and the main transformer was located below the body, between the bogies, lowering the centre of gravity, and assisting in the reduction of body roll, and relative pantograph movement.
The traction motors, as mentioned above, are body mounted, but slung below the floor, in the bogie space, which in turn, has enabled a more or less conventional layout of equipment on board. The transmission features a coupling arrangement patented by GEC Traction, with the motors driving the wheelsets through a right-angle gearbox, and bevel gears. The hollow output shaft of the gearbox drives the wheels through a rubber bushed link coupling, isolating the drive from relative radial and lateral movement of the wheelsets imparted by the primary suspension. Each traction motor was fitted with a ventilated disc brake at the inboard end.
The major characteristics of the Class 91 are detailed below;
| Wheel arrangement | Bo-Bo |
| Track gauge | standard |
| Overall length | 19400 mm |
| Overall height | 3757 mm |
| Overall width | 2740 mm |
| Max service speed | 240 km/hr |
| Weight in working order | 80 tonnes |
| Unsprung mass per axle | 1.7 tonnes |
| Line voltage | 25kV a.c. |
| Bogie wheelbase | 3350 mm |
| Bogie pivot centres | 10500 mm |
| Wheel diameter (new) | 1220 mm |
| Max tractive effort | 55440 kg |
| Cont tractive effort | 39040 kg |
| Max power at rail | 4700 kW |
| Continuous power | 4530 kW |
| Brakes – locomotives | air |
| – train | air |
The class 91 order included an option for a further 25, and featured a double ended design, but with only the No.1 end having any degree of aerodynamic styling. In normal service, during the day, the streamlined end would normally be at the end of the train, pulling when running in one direction, and pushing, when running in the opposite direction. When pushing, control signals are transmitted to the Driving Van Trailer (DVT) attached to the opposite end of the train, by means of Time Division Multiplex (TDM) signals, sent along train wires, on board. The No.2 end cab is flat faced, and a profile that matched the profile of the adjoining coaches was adopted. The non-streamlined end would be used normally when the locomotives were running semi-fast, sleeper services, or other non high speed duties.
Interestingly, the class 91 was designed for a 35-year working life, averaging 420,000 km per year, which meant that in a couple of years’ time – 2023 – we would be saying goodbye to this impressive locomotive. But of course, events have turned out rather differently, and privatisation has created a much more complex operating environment, for both the technology of the train, and the management of the railway.
Sadly – although this year marks the 30th anniversary of its use on the WCML – they were never used in anger there, and by the turn of the century, the ‘Pendolino’ had arrived – by way of Fiat, Alstom and Metro-Cammell. There too, the technology developed at BR’s Derby Research Centre played its part in the late 1970s and into 1980, with the APT – but that’s a story for another day.
-oOo-
Useful links
https://en.wikipedia.org/wiki/British_Rail_Class_91
https://en.wikipedia.org/wiki/Brecknell_Willis_high_speed_pantograph
