British Rail Class 70
Encyclopedia
The British Rail Class 70 was a class of three 3rd rail Co-Co electric locomotive
s. The initial two were built by the Southern Railway
at Ashford Works
in 1941 and 1945 and were numbered CC1 and CC2. Electrical equipment was designed by Alfred Raworth and the body by Oliver Bulleid
. CC2 was modified slightly from the original design by C. M. Cock who had succeeded Raworth as Electrical Engineer. The third was built by British Railways in 1948 and numbered 20003.
multiple unit
design. It has even been suggested that (in true Southern tradition) this was because the jigs for the welded cabs already existed and thus made for speedy and cheap construction. At the outbreak of war
in 1939, most construction projects were put on hold in favour of the war effort. Construction of CC1 and CC2 was exempted from this because of promised savings in labour and fuel over steam locomotives. Construction was not smooth however and was brought to a halt several times due to shortage of resource.
. S. B. Warder (later to become Chief Electrical Engineer of the British Transport Commission
and architect of the 25 kV AC overhead system still in use today) was by then SR Electrical Engineer and he modified the design somewhat. Although counted as the same class, 20003 was markedly different externally to its two earlier sisters, being 2 inches (5 cm) longer with flat 4SUB
-like cab ends, arguably simpler (and therefore cheaper) design than the earlier two. Equipment changes added 5 tons to the earlier 100-ton design.
, but as it quickly became apparent that suitable headcodes for freight workings did not exist (nor did the combination of two numbers only at that time, provide the scope) they were also fitted with six steam locomotive style discs at each end so that standard codes could be displayed. With standardisation came a whole set of new two-character codes with letters as well, and all three locomotives were fitted with roller-blind headcodes and the discs removed.
s providing 1470 hp allowed them to handle 1000-ton freight and 750-ton passenger trains with ease.
set with a large flywheel
on the shaft between the two. The traction current, instead of feeding the traction motors directly through the control assembly, powered a large motor which turned a shaft with the flywheel and fed into the generator. The output of the generator could be combined with the 3rd rail power to reduce or boost the voltage applied to the traction motors. With the generator output polarity reversed, the control assembly could deliver around 1200 V DC by combining the generator output with the 650 V from the 3rd rail to give positive 650 V and negative 500-600 V - leading to the nickname "boosters"
. The flywheel ensured the generator continued to turn whilst no current was available from the 3rd rail, thus ensuring a continuous supply to the traction motors.
Even while stationary, Class 70 produced a noticeable droning noise due to the generator turning inside the body. Two booster sets were fitted in each locomotive, one for each bogie. It was not sufficient to allow the locomotives to work "off the juice" as the load on the generator whilst under power meant it would quickly consume the stored kinetic energy
. They needed attentive driving, to ensure they were not brought to a halt on a gap and the booster set allowed to run down.
There were losses incurred in the conversion of electrical energy to kinetic and back again, but Raworth mitigated this in the control mechanism. Instead of having large, heavily built resistances in the power lines for the motors, the 26 taps on the throttle changed resistances in the field coils of the generator. These correspondingly made the construction much lighter and more easily maintained. Instead of "burning-up" unrequired power, the throttle simply altered how much power was generated.
to allow them to work from overhead lines
erected in some yards (notably Hither Green
, South East London
) where it was deemed too dangerous to have 3rd rail with staff constantly at track level, particularly in wartime blackout. The pantograph was recessed into a cut-out on the roof when not in use, to keep within the loading gauge.
The locomotives were fitted with electrically powered train heating boilers
to generate steam for train heating.
, which used the same concept, the latter differed greatly in its design and construction, being based on Swiss practice.
All three were withdrawn in the winter of 1968/1969 without receiving TOPS
numbers, although 20001 received BR corporate blue for its final years. None survived to preservation.
Electric locomotive
An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage device...
s. The initial two were built by the Southern Railway
Southern Railway (Great Britain)
The Southern Railway was a British railway company established in the 1923 Grouping. It linked London with the Channel ports, South West England, South coast resorts and Kent...
at Ashford Works
Ashford railway works
Ashford railway works was in the town of Ashford in the county of Kent in England.-South Eastern Railway:Ashford locomotive works was built by the South Eastern Railway on a new site in 1847, replacing an earlier locomotive repair facility at New Cross in London...
in 1941 and 1945 and were numbered CC1 and CC2. Electrical equipment was designed by Alfred Raworth and the body by Oliver Bulleid
Oliver Bulleid
Oliver Vaughan Snell Bulleid was a British railway and mechanical engineer best known as the Chief Mechanical Engineer of the Southern Railway between 1937 and the 1948 nationalisation, developing many well-known locomotives.- Early life and Great Northern Railway :He was born in Invercargill,...
. CC2 was modified slightly from the original design by C. M. Cock who had succeeded Raworth as Electrical Engineer. The third was built by British Railways in 1948 and numbered 20003.
Southern Railway nos. CC1 and CC2
Externally, it was clear the cab design owed a lot to Southern experience with the 2HALBritish Rail Class 402
The Southern Railway gave the designation 2-HAL to the electric multiple units built during the late 1930s to work long-distance semi-fast services on the newly electrified lines from London to Maidstone and Gillingham...
multiple unit
Multiple unit
The term multiple unit or MU is used to describe a self-propelled carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. The term is commonly used to denote passenger trainsets consisting of more than one carriage...
design. It has even been suggested that (in true Southern tradition) this was because the jigs for the welded cabs already existed and thus made for speedy and cheap construction. At the outbreak of war
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
in 1939, most construction projects were put on hold in favour of the war effort. Construction of CC1 and CC2 was exempted from this because of promised savings in labour and fuel over steam locomotives. Construction was not smooth however and was brought to a halt several times due to shortage of resource.
British Railways no. 20003
After nationalisation in 1948, British Railways renumbered them 20001 and 20002 respectively. the third member of the class, 20003 from new, was built at BrightonBrighton railway works
Brighton railway works was one of the earliest railway-owned locomotive repair works, founded in 1840 by the London and Brighton Railway in Brighton, England, and thus pre-dating the more famous railway works at Crewe, Doncaster and Swindon...
. S. B. Warder (later to become Chief Electrical Engineer of the British Transport Commission
British Transport Commission
The British Transport Commission was created by Clement Attlee's post-war Labour government as a part of its nationalisation programme, to oversee railways, canals and road freight transport in Great Britain...
and architect of the 25 kV AC overhead system still in use today) was by then SR Electrical Engineer and he modified the design somewhat. Although counted as the same class, 20003 was markedly different externally to its two earlier sisters, being 2 inches (5 cm) longer with flat 4SUB
British Rail Class 405
Under the British Rail TOPS computer system, Class 415 was allocated to surviving examples of the Southern Railway 4-Sub Class electric multiple units built between 1941 and 1951...
-like cab ends, arguably simpler (and therefore cheaper) design than the earlier two. Equipment changes added 5 tons to the earlier 100-ton design.
Headcodes
All three locomotives were equipped with stencil headcodesTrain reporting number
A train reporting number is used by railway staff in Great Britain to identify a particular train service. It consists of:* A single-digit number, indicating the class of train* A letter, indicating the destination area...
, but as it quickly became apparent that suitable headcodes for freight workings did not exist (nor did the combination of two numbers only at that time, provide the scope) they were also fitted with six steam locomotive style discs at each end so that standard codes could be displayed. With standardisation came a whole set of new two-character codes with letters as well, and all three locomotives were fitted with roller-blind headcodes and the discs removed.
Technical details
The class soon proved their worth. The six traction motorTraction motor
Traction motor refers to an electric motor providing the primary rotational torque of a machine, usually for conversion into linear motion ....
s providing 1470 hp allowed them to handle 1000-ton freight and 750-ton passenger trains with ease.
Booster control
Being much shorter than the predominant multiple units, electric locomotives can suffer from a problem known as "gapping" - becoming marooned between supplies at breaks in the 3rd rail electrical supply, snatching at the couplings whilst moving as they come on and off the power. The latter places undue stress on couplings and has been known to cause separations of a train. Raworth overcame this by having a motor-generatorMotor-generator
A motor-generator is a device for converting electrical power to another form. Motor-generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line...
set with a large flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...
on the shaft between the two. The traction current, instead of feeding the traction motors directly through the control assembly, powered a large motor which turned a shaft with the flywheel and fed into the generator. The output of the generator could be combined with the 3rd rail power to reduce or boost the voltage applied to the traction motors. With the generator output polarity reversed, the control assembly could deliver around 1200 V DC by combining the generator output with the 650 V from the 3rd rail to give positive 650 V and negative 500-600 V - leading to the nickname "boosters"
Booster (electric power)
A Booster was a motor-generator set used for voltage regulation in direct current electrical power circuits. The development of alternating current and solid-state devices has rendered it obsolete...
. The flywheel ensured the generator continued to turn whilst no current was available from the 3rd rail, thus ensuring a continuous supply to the traction motors.
Even while stationary, Class 70 produced a noticeable droning noise due to the generator turning inside the body. Two booster sets were fitted in each locomotive, one for each bogie. It was not sufficient to allow the locomotives to work "off the juice" as the load on the generator whilst under power meant it would quickly consume the stored kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
. They needed attentive driving, to ensure they were not brought to a halt on a gap and the booster set allowed to run down.
There were losses incurred in the conversion of electrical energy to kinetic and back again, but Raworth mitigated this in the control mechanism. Instead of having large, heavily built resistances in the power lines for the motors, the 26 taps on the throttle changed resistances in the field coils of the generator. These correspondingly made the construction much lighter and more easily maintained. Instead of "burning-up" unrequired power, the throttle simply altered how much power was generated.
Other features
All three were fitted with a tram-style pantographPantograph (rail)
A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...
to allow them to work from overhead lines
Overhead lines
Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses or trains at a distance from the energy supply point...
erected in some yards (notably Hither Green
Hither Green
Hither Green is a district in south east London, England, located in the London Borough of Lewisham. It is situated 6.6 miles south east of Charing Cross, and on the Prime Meridian....
, South East London
South East (London sub region)
The South East is a sub-region of the London Plan corresponding to the London Boroughs of Bexley, Bromley, Greenwich, Lewisham and Southwark. The sub region was established in 2008. The south east has a population of 1,300,000 and is the location of 500,000 jobs...
) where it was deemed too dangerous to have 3rd rail with staff constantly at track level, particularly in wartime blackout. The pantograph was recessed into a cut-out on the roof when not in use, to keep within the loading gauge.
The locomotives were fitted with electrically powered train heating boilers
Steam generator (railroad)
Steam generator is the term used to describe a type of boiler used to produce steam for climate control and potable water heating in railroad passenger cars...
to generate steam for train heating.
Successor and withdrawal
The class formed a "proof-of-concept" for booster-based electric locomotives. Although thought of as prototypes for the later Class 71British Rail Class 71
The British Rail Class 71 was an electric locomotive used on the Southern Region of British Railways, unlike most other Southern Region electric locomotives they could not operate away from the electrified system.- History :As part of the BTC Modernisation Plan of 1955, twenty-four electric...
, which used the same concept, the latter differed greatly in its design and construction, being based on Swiss practice.
All three were withdrawn in the winter of 1968/1969 without receiving TOPS
TOPS
Total Operations Processing System, or TOPS, is a computer system for managing the locomotives and rolling stock owned by a rail system...
numbers, although 20001 received BR corporate blue for its final years. None survived to preservation.