British Rail Class 74
Encyclopedia
British Rail Class 74 was an electro-diesel locomotive
that operated on the Southern Region of British Railways
, rebuilt from redundant Class 71
locomotives in the late 1960s. An electro-diesel locomotive is one that can operate either from an electrical supply
, such as overhead catenary or (in this case) an energised third rail, or from an onboard diesel engine
.
(pre-TOPS
type HA) were built in 1958 at the British Rail
works in Doncaster
and in 1964 ten were deemed surplus to requirements, withdrawn from service and placed in storage. The Southern Region was highly impressed with the "little-ED" JA & JB/class 73
locomotives and were keen to see a higher power locomotive with the same flexibility. In 1965, discussions were opened with English Electric
(builders of the production JB/Class 73) to produce a high powered electro-diesel. Originally a centre-cab locomotive was envisaged similar in concept to the Clayton
Class 17
but details on this are scant. This design was not pursued - possibly due to the historical frugality of the SR and the availability of the ten moth-balled members of Class 71. These were moved in groups to the British Rail works at Crewe
, where they were rebuilt into type HB/Class 74 electro-diesels. Buckeye couplers
and high-level control & brake jumpers were fitted to facilitate working with other EP stock
- especially TC
units in push-pull
mode. Also, two-tone "raspberry" air horns were mounted on the cab roof, replacing the original air whistle of Class 71 locomotives.
They were intended especially for use on the boat train
s to Southampton
and Weymouth
, as both routes included sections of non-electrified track and tramway along the public thoroughfare
. The elimination of the locomotive change (at either Eastleigh (for Southampton) or Bournemouth
) was envisaged and their dual power capability would greatly accelerate timings and reduce operational requirements.
Originally, plans had been to number them E7001-E7010, but once rebuilt they were numbered E6101-E6110 instead. Later they were renumbered 74001-74010 under the TOPS
system.
), Class 74 utilised a booster
set (a motor-generator and flywheel combination) to overcome the problem of gapping. Booster set 836/2D had been designed by English Electric for use in Class 71 and this was retained in the rebuild, although weight considerations meant that the flywheel
assembly, separate auxiliary generator and traction motor blowers were removed (the latter leading to the decision to downrate the traction motors). The compact size of the booster permitted a small diesel engine and generator inside the body shell (only a single booster was used in Classes 71 & 74 unlike the two of Class 70
). Thus, these locomotives could operate either from a third rail supply at 650 V DC (Eastern & Central sections), 750 V DC (Western section) or from their Paxman
6YJXL 'Ventura' diesel engine, pressed to just 650 hp
- well within the engine's stress curve and thus greatly extending service intervals. This choice of engine (despite its problems as employed in Class 74) was a good move. 57 of these engines had been supplied for use in Class 14
and a further 20 had been supplied to Scottish workshops of BR for the re-engining program of Class 21
(such locomotives being designated Class 29
). Thus a proven track record and a plentiful supply of spares was assured. The Class 71 pantograph
for overhead current collection was dispensed with.
supply controlled by rectifier
s requires an AC
power source. Consequently, the existing auxiliary generator
was converted to a three-phase alternator
with automatic voltage regulator. This arrangement gives improved control of traction current over conventional rheostatic systems and gives fine control when starting a train. Normally the driver has to maintain tractive effort
well below the rail adhesion limit to give himself time to respond to wheel slip. The constant current systems of Class 74 were designed to allow the driver to apply power very near the limit of adhesion and the booster output is regulated in such a way that the maximum current of any traction motor group does not exceed the selected value. Thus, even when one motor (axle, wheel set) starts slipping, the voltage across the whole group of motors cannot rise because current in the non-slipping motors is fixed. As one motor begins to slip, its current consumption drops (electric motors use greatest current when stalled and least while free-running) which provides more current for the non-slipping motor (The current for the group is fixed and therefore shared across the motors in the group). The voltage drops proportionately and the slipping motor now partly deprived of power, begins to slow, the slip stops and everything returns to the state it was in before slip set in. Simply speaking the motors all work as a differentially balanced team so that as one motor begins to slip, the others act to balance everything which reduces the speed of the slipping motor almost 'by magic', but maintains torque at a point just below the friction break-away point. Recovery of wheel slip (providing the driver is not in-attentive or deliberately attempting to slip) is very rapid. It is this system that allowed the incredible acceleration for which Class 74 was known.
The power controller allowed infinite variability but standard notches were provided so Class 74 locomotives could work with their smaller sisters, Class 73/1, or with any electro-pneumatically controlled (blue star coupling code) Type 2, 3 or 4 diesel locomotive. Two constant voltage notches were provided for slow speed control of shunting and coupling-up. Three further notches spaced out over the power range corresponded to the 'Series, Parallel, Weak-Field' (2, 3 & 4) settings of power controllers in multiple unit stock.
Control equipment was based around the 'Line Replaceable Unit' (LRU) ethos and consisted of 'trays' of circuit boards and equipment arranged in two cabinets. No.1 housed just the usual circuit breaker
s, relay
s, reversers and so forth. No.2 also housed standard equipment but included the complex electronic control circuits that ultimately were the un-doing of the class. Each tray could be slid in and out of the cabinet (with the locomotive switched off) with ease and each had a test connector. Specific testers were made that simply compared the electrical signals and stimuli on the test socket with the design values. If any were not as expected, the whole tray was replaced and the locomotive was good-to-go... at least that was the theory. The use of testers plugged into the test socket removed the need for engineering staff to be competent electronic engineers (as opposed to electrical engineers which they undoubtedly were), but often faults on one tray would only show themselves in combination with faults on other trays. This led to confusing diagnostics and locomotives were often failed for long periods pending in-depth exploration of a fault. Faulty trays were sent for repair. This early attempt was bold and fundamentally sound. Electronic circuit arrangements in modern locomotives use this approach almost unchanged. Unfortunately, powerful control and computational electronics were in their infancy in 1968. Had the resources of just ten years later been available, it is arguable that Class 74 would have been a success.
framework with outriggers to support the curved body skin. Translucent roof panels were fitted to increase daytime illumination in the engine room - to great effect.
One might think putting a diesel engine into an electric locomotive with a booster set is simply a matter of coupling the crankshaft of the engine to the main shaft of the existing booster through some clutch/gearbox arrangement, but this was not so. When working on diesel power, the engine drove generator EE843/1C (615 V output) direct to the booster power input. It must not, however, be thought that the 615 V input was a direct replacement of the conventional electric supply - the configuration of the booster set did not work simply by replacing the line voltage. See the article on Boosters
for clarification. The equipment train of Engine+Generator+Booster proved too long with the existing equipment layout. Modifications were made (cooler groups, water tanks and silencer were mounted in roof sections over the equipment room) and very little of the progenitor locomotive layout remained. All was well with production back on track.
' units were built in 1973/74, class 74 had regular daytime passenger turns including the 15:30 Waterloo-Weymouth (as far as Bournemouth). Subsequently their only regular non-freight workings were on night mail and newspaper trains to and from Bournemouth and the Weymouth boat trains.
In practice, Class 74 was a rare visitor to Weymouth (because failures on diesel were common and a stranded train, irate passengers and blocked line are highly undesirable) and was usually replaced at Bournemouth by the redoubtable Class 33
for the final leg of the journey. This was almost directly attributable to their problems when running on diesel power and totally negated their raison d'être. Quite simply; they were not trusted and as a result, they failed to deliver the expected advantages of a higher power (than Class 73) electro-diesel. Services to Southampton Ocean terminal did use them frequently over non-electrified lines, but this required only a few miles of diesel haulage rather than 60+ on the trip to Weymouth and back. Also, following the closure of Southampton Terminus Station
, the section of non-electrified track served Ocean Terminal exclusively - a failure here would not inconvenience other services - the same was not true West of Bournemouth. The steep ascent from Weymouth would also have taxed their 650 HP diesel output to the utmost, as the 'Channel Islands Boat Train' usually loaded to 11 cars.
Class 73 had a simpler electrical system arrangement for control of the dual power sources - even to the point of two separate power controllers on the driver's desk; one for diesel and one for electric. The complex control system of Class 74 (with one dual-purpose controller) was problematic and the class was dogged with electrical system failures up to their last days. Together, the three complaints of poor reliability, difficult engine starting and excessive noise made Class 74 unpopular with crew and fitters alike.
When in good order they were sprightly performers and running on third rail with the full 2552 hp brought to bear (the original class 71 traction equipment having been down-rated slightly from 2700 hp to extend service intervals), many runs in excess of 100 miles per hour (160.9 km/h) were noted despite a stated maximum of 90 miles per hour (144.8 km/h) - though nothing approaching this was achievable on diesel power. Their electronic power delivery meant that acceleration was equally impressive on both diesel and electric power sources. Running on the diesel engine however, available power was pretty much exhausted by the time 60 miles per hour (96.6 km/h) or 70 miles per hour (112.7 km/h) was reached with 'normal' loads and heavy loads (even 8 or nine loaded milk tanks over the banks of the West London Line) would tax them. Speeds would drop and recovery margins in timings taken full advantage of.
They were regular visitors to the London area, often running on Midland
and Western Region
tracks. In the early half of the 1970s, milk trains for the Southern Region were a staple for the class as far as Acton Yard, requiring diesel power from Clapham Junction
through Kensington and onto the Western Region mainline (Class 52
or occasionally Class 47
were used for the major haul west of Acton to and from Cornwall and Devon). This would usually produce two trains per weekday and often two different examples of the class. These trains were of note as they often included Diesel Brake Tenders (DBT - basically heavy, weighted bogie wagons with vacuum brakes) to assist with available braking effort.
Although their multiple working abilities allowed them to control (with a single crew) each other, Class 73, EP multiple unit stock and any blue star coded mainline diesel locomotive, multiple operations were exceptionally rare. Wherever Class 74 was noted with another locomotive, the '74 would invariably be 'dead in-train' - i.e. failed and subsequently rescued. One exception to this were the frequent balancing runs between their home depot of Eastleigh and their day-time out-stations of either Clapham Junction yard or Stewarts Lane depot in readiness for night-time postal and newspaper trains from Waterloo. These were nearly always light-engine or occasionally combined with empty coaching stock (ECS) moves with both locomotives under power - over 5000 hp.
The entire class was allocated to Eastleigh
depot for their operational life and 74003 was the last locomotive to enter Eastleigh works for repairs. In common with Class 73, Class 74 was sent to Crewe
for heavy maintenance up until 1972, when Eastleigh took over all treatment of both classes.
Although at this time, the electronic control problems of the class could have been resolved (by virtue of the evolution of electronics) and British Rail had demonstrated a willingness to undertake heavy re-design work on other locomotive types to improve reliability (notably on Classes 82
, 83
& 84
) the work for which the class had been built was drying up. Boat trains were greatly reduced in number and many of the remaining were replaced with multiple units. Freight and parcel work was contracting and Class 74 was embarrassingly short of work (as was the progenitor Class 71), due purely to the changing tides and fortunes of the railway business. In July 1977, 74002 was withdrawn following a collision and a month later, 74009 failed and budgetary permission to repair was not forthcoming. On the last day of 1977 the seven remaining members of class 74 (and all 14 members of Class 71) were withdrawn from traffic. They languished at Eastleigh depot for almost a year until all but 74010 were stripped of reusable components and dispatched to various scrap yards. 74004 & 74009 remained at Long Marston
until August 1978 whence they were reduced to scrap. 74005 was the last surviving member of the class being finally broken-up in January 1981 at Fratton near Portsmouth
not far from its home depot.
depot for evaluation as a potential candidate for departmental use at the Railway Technical Centre
and remained in the depot yard for some time. Despite being in fully working order with a mass of spares available (from sister locomotives now scrapped) it was eventually deemed unsuitable, towed to Doncaster
and scrapped in 1979.
Electro-diesel locomotive
An Electro-diesel locomotive is powered either from an electricity supply or by using the onboard diesel engine...
that operated on the Southern Region of British Railways
Southern Region of British Railways
The Southern Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992. The region covered south London, southern England and the south coast, including the busy commuter belt areas of Kent, Sussex...
, rebuilt from redundant Class 71
British 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...
locomotives in the late 1960s. An electro-diesel locomotive is one that can operate either from an electrical supply
Railway electrification system
A railway electrification system supplies electrical energy to railway locomotives and multiple units as well as trams so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world...
, such as overhead catenary or (in this case) an energised third rail, or from an onboard diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
.
History
Twenty-four examples of British Rail 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...
(pre-TOPS
TOPS
Total Operations Processing System, or TOPS, is a computer system for managing the locomotives and rolling stock owned by a rail system...
type HA) were built in 1958 at the British Rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...
works in Doncaster
Doncaster Works
Doncaster railway works is in the town of Doncaster, South Yorkshire, England.Always referred to as "the Plant", it was established by the Great Northern Railway in 1853, replacing the previous works in Boston and Peterborough...
and in 1964 ten were deemed surplus to requirements, withdrawn from service and placed in storage. The Southern Region was highly impressed with the "little-ED" JA & JB/class 73
British Rail Class 73
The British Rail Class 73 is a United Kingdom model of electro-diesel locomotive. The type is unusual in that it can operate from a 750 V DC third-rail or an on-board diesel engine to allow it to operate on non-electrified routes...
locomotives and were keen to see a higher power locomotive with the same flexibility. In 1965, discussions were opened with English Electric
English Electric
English Electric was a British industrial manufacturer. Founded in 1918, it initially specialised in industrial electric motors and transformers...
(builders of the production JB/Class 73) to produce a high powered electro-diesel. Originally a centre-cab locomotive was envisaged similar in concept to the Clayton
Clayton Equipment Company
Clayton Equipment Company Ltd, now known simply as Clayton Equipment Ltd or CEC and CEL, is a locomotive construction company that specialises in locomotives for underground mining operations.-Inception:...
Class 17
British Rail Class 17
The British Rail Class 17 was a class of 117 Bo-Bo diesel-electric locomotives built 1962–1965 by Clayton Equipment Company and their sub-contractor Beyer, Peacock & Co., for British Railways ....
but details on this are scant. This design was not pursued - possibly due to the historical frugality of the SR and the availability of the ten moth-balled members of Class 71. These were moved in groups to the British Rail works at Crewe
Crewe Works
Crewe railway works is a British railway engineering facility built in 1840 by the Grand Junction Railway. It is located in the town of Crewe, in the county of Cheshire....
, where they were rebuilt into type HB/Class 74 electro-diesels. Buckeye couplers
Janney coupler
The Janney coupler, also known as a knuckle coupler, buckeye coupler, alliance coupler and AAR coupler is an automatic coupler patented by Eli H...
and high-level control & brake jumpers were fitted to facilitate working with other EP stock
Electro-pneumatic brake system on British railway trains
The Electro-pneumatic brake system on British railway trains was introduced in 1950. The Southern Region of British Railways operated an intensive self-contained fleet of electric multiple units for suburban and middle distance passenger trains...
- especially TC
British Rail Class 438
The British Rail TC multiple units were un-powered fixed formations of 3 or 4 carriages with a driving position at each end of the set, converted by BR at York Works from locomotive-hauled Mark 1 carriages in 1966-1967 and 1974. The units built on experience gained from the prototype 6TC unit...
units in push-pull
Push-pull train
Push–pull is a mode of operation for locomotive-hauled trains allowing them to be driven from either end.A push–pull train has a locomotive at one end of the train, connected via some form of remote control, such as multiple-unit train control, to a vehicle equipped with a control cab at the other...
mode. Also, two-tone "raspberry" air horns were mounted on the cab roof, replacing the original air whistle of Class 71 locomotives.
They were intended especially for use on the boat train
Boat train
A boat train is a passenger train which connects with a passenger ship, such as a ferry or ocean liner. Through ticketing is normally available. -Notable named boat trains:*The Flèche d'Or Paris Gare du Nord to Calais...
s to Southampton
Southampton Terminus railway station
Southampton Terminus railway station served the docks and city centre of Southampton, England. The station was first authorized on the 25 July 1834, it began as the terminus of the London and South Western Railway...
and Weymouth
Weymouth Quay railway station
Weymouth Quay is a disused railway station in Weymouth, Dorset, England at the terminus of the Weymouth Harbour Tramway. Until September 1987 it was the regular terminus and starting point for boat trains, linking to the ferry services with street running along the streets of the town.After the...
, as both routes included sections of non-electrified track and tramway along the public thoroughfare
Weymouth Harbour Tramway
The Weymouth Harbour Tramway is a goods and passenger railway constructed almost entirely on the streets of Weymouth, England...
. The elimination of the locomotive change (at either Eastleigh (for Southampton) or Bournemouth
Bournemouth railway station
Bournemouth railway station, originally known as Bournemouth East and then Bournemouth Central , is the main railway station serving the town of Bournemouth in Dorset, England. It is located on the South Western Main Line from London Waterloo to Weymouth...
) was envisaged and their dual power capability would greatly accelerate timings and reduce operational requirements.
Originally, plans had been to number them E7001-E7010, but once rebuilt they were numbered E6101-E6110 instead. Later they were renumbered 74001-74010 under the TOPS
TOPS
Total Operations Processing System, or TOPS, is a computer system for managing the locomotives and rolling stock owned by a rail system...
system.
Power supply
In common with the first SR DC electric locomotives (Class 70British Rail Class 70
The British Rail Class 70 was a class of three 3rd rail Co-Co electric locomotives. 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...
), Class 74 utilised a booster
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...
set (a motor-generator and flywheel combination) to overcome the problem of gapping. Booster set 836/2D had been designed by English Electric for use in Class 71 and this was retained in the rebuild, although weight considerations meant that the 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...
assembly, separate auxiliary generator and traction motor blowers were removed (the latter leading to the decision to downrate the traction motors). The compact size of the booster permitted a small diesel engine and generator inside the body shell (only a single booster was used in Classes 71 & 74 unlike the two of Class 70
British Rail Class 70
The British Rail Class 70 was a class of three 3rd rail Co-Co electric locomotives. 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...
). Thus, these locomotives could operate either from a third rail supply at 650 V DC (Eastern & Central sections), 750 V DC (Western section) or from their Paxman
Paxman (engines)
Paxman is a major British brand of diesel engines. Ownership has changed on a number of occasions since the company's formation in 1865, and now the brand is owned by MAN SE, as part of MAN Diesel & Turbo. At its peak, the Paxman works covered 23 acres and employed over 2,000 people. Engine...
6YJXL 'Ventura' diesel engine, pressed to just 650 hp
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
- well within the engine's stress curve and thus greatly extending service intervals. This choice of engine (despite its problems as employed in Class 74) was a good move. 57 of these engines had been supplied for use in Class 14
British Rail Class 14
The British Rail Class 14 is a type of small diesel-hydraulic locomotive built in the mid-1960s. Twenty-six of these 0-6-0 locomotives were ordered in January 1963, to be built at British Railways Swindon Works. The anticipated work for this class was yard shunting, trip work and short distance...
and a further 20 had been supplied to Scottish workshops of BR for the re-engining program of Class 21
British Rail Class 21
The British Rail Class 21 was a type of Type 2 diesel-electric locomotive built by the North British Locomotive Company in Glasgow for British Railways in 1958-1960....
(such locomotives being designated Class 29
British Rail Class 29
The British Rail Class 29 were a class of 20 diesel-electric Bo'Bo' locomotives produced by the re-engining of the British Rail Class 21 units. The units were designed for both passenger and freight trains...
). Thus a proven track record and a plentiful supply of spares was assured. The Class 71 pantograph
Pantograph (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...
for overhead current collection was dispensed with.
Electronic traction control
Obtaining a DCDirect current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
supply controlled by rectifier
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
s requires an AC
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
power source. Consequently, the existing auxiliary generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
was converted to a three-phase alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
with automatic voltage regulator. This arrangement gives improved control of traction current over conventional rheostatic systems and gives fine control when starting a train. Normally the driver has to maintain tractive effort
Tractive effort
As used in mechanical engineering, the term tractive force is the pulling or pushing force exerted by a vehicle on another vehicle or object. The term tractive effort is synonymous with tractive force, and is often used in railway engineering to describe the pulling or pushing capability of a...
well below the rail adhesion limit to give himself time to respond to wheel slip. The constant current systems of Class 74 were designed to allow the driver to apply power very near the limit of adhesion and the booster output is regulated in such a way that the maximum current of any traction motor group does not exceed the selected value. Thus, even when one motor (axle, wheel set) starts slipping, the voltage across the whole group of motors cannot rise because current in the non-slipping motors is fixed. As one motor begins to slip, its current consumption drops (electric motors use greatest current when stalled and least while free-running) which provides more current for the non-slipping motor (The current for the group is fixed and therefore shared across the motors in the group). The voltage drops proportionately and the slipping motor now partly deprived of power, begins to slow, the slip stops and everything returns to the state it was in before slip set in. Simply speaking the motors all work as a differentially balanced team so that as one motor begins to slip, the others act to balance everything which reduces the speed of the slipping motor almost 'by magic', but maintains torque at a point just below the friction break-away point. Recovery of wheel slip (providing the driver is not in-attentive or deliberately attempting to slip) is very rapid. It is this system that allowed the incredible acceleration for which Class 74 was known.
The power controller allowed infinite variability but standard notches were provided so Class 74 locomotives could work with their smaller sisters, Class 73/1, or with any electro-pneumatically controlled (blue star coupling code) Type 2, 3 or 4 diesel locomotive. Two constant voltage notches were provided for slow speed control of shunting and coupling-up. Three further notches spaced out over the power range corresponded to the 'Series, Parallel, Weak-Field' (2, 3 & 4) settings of power controllers in multiple unit stock.
Control equipment was based around the 'Line Replaceable Unit' (LRU) ethos and consisted of 'trays' of circuit boards and equipment arranged in two cabinets. No.1 housed just the usual circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s, relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
s, reversers and so forth. No.2 also housed standard equipment but included the complex electronic control circuits that ultimately were the un-doing of the class. Each tray could be slid in and out of the cabinet (with the locomotive switched off) with ease and each had a test connector. Specific testers were made that simply compared the electrical signals and stimuli on the test socket with the design values. If any were not as expected, the whole tray was replaced and the locomotive was good-to-go... at least that was the theory. The use of testers plugged into the test socket removed the need for engineering staff to be competent electronic engineers (as opposed to electrical engineers which they undoubtedly were), but often faults on one tray would only show themselves in combination with faults on other trays. This led to confusing diagnostics and locomotives were often failed for long periods pending in-depth exploration of a fault. Faulty trays were sent for repair. This early attempt was bold and fundamentally sound. Electronic circuit arrangements in modern locomotives use this approach almost unchanged. Unfortunately, powerful control and computational electronics were in their infancy in 1968. Had the resources of just ten years later been available, it is arguable that Class 74 would have been a success.
Complications with rebuild
The body of HA/Class 71 locomotives was never intended to carry any weight, the construction following typical, steam-experience methods for the 1950s of massive under-frames with the body perched on top to stop everything getting wet. In August 1966, after initial strip-down and examination of E5016, engineers were forced to re-assess the build when it became apparent the planned equipment changes could not be accommodated. It was even mooted that the body would have to be divided and lengthened. The additional weight (even after dispensing with the flywheel and other heavy equipment) meant the body had to be re-constructed and stressed by use of Warren girderGirder
A girder is a support beam used in construction. Girders often have an I-beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams...
framework with outriggers to support the curved body skin. Translucent roof panels were fitted to increase daytime illumination in the engine room - to great effect.
One might think putting a diesel engine into an electric locomotive with a booster set is simply a matter of coupling the crankshaft of the engine to the main shaft of the existing booster through some clutch/gearbox arrangement, but this was not so. When working on diesel power, the engine drove generator EE843/1C (615 V output) direct to the booster power input. It must not, however, be thought that the 615 V input was a direct replacement of the conventional electric supply - the configuration of the booster set did not work simply by replacing the line voltage. See the article on 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...
for clarification. The equipment train of Engine+Generator+Booster proved too long with the existing equipment layout. Modifications were made (cooler groups, water tanks and silencer were mounted in roof sections over the equipment room) and very little of the progenitor locomotive layout remained. All was well with production back on track.
Operations
The Paxman engine of Class 74 was marginally more powerful than Class 73s English Electric engine but it was nowhere near as reliable. The Paxman was also noisy (due to the silencer mounted in the roof very near the cab) and difficult to start on occasion - rather negating the novel change-over whilst in motion and subsequent flexibility off the third rail. The class's generally poor reliability often led to (unscheduled) electric to diesel changeovers when on the move; regular passengers on Class 74-hauled passenger trains became quite used to this. Until four additional '4-REPBritish Rail Class 432
The British Rail 4-REP electric multiple units were built by BR at York Works from 1966-1967 and 1974. The units were built to power the 4-TC trailer units on services on the South Western Main Line. Fifteen four-car units were eventually built. The motor coaches were new build, but the trailers...
' units were built in 1973/74, class 74 had regular daytime passenger turns including the 15:30 Waterloo-Weymouth (as far as Bournemouth). Subsequently their only regular non-freight workings were on night mail and newspaper trains to and from Bournemouth and the Weymouth boat trains.
In practice, Class 74 was a rare visitor to Weymouth (because failures on diesel were common and a stranded train, irate passengers and blocked line are highly undesirable) and was usually replaced at Bournemouth by the redoubtable Class 33
British Rail Class 33
The British Rail Class 33 also known as the BRCW Type 3 or Crompton is a class of Bo-Bo diesel-electric locomotives ordered in 1957 and built for the Southern Region of British Railways between 1960 and 1962....
for the final leg of the journey. This was almost directly attributable to their problems when running on diesel power and totally negated their raison d'être. Quite simply; they were not trusted and as a result, they failed to deliver the expected advantages of a higher power (than Class 73) electro-diesel. Services to Southampton Ocean terminal did use them frequently over non-electrified lines, but this required only a few miles of diesel haulage rather than 60+ on the trip to Weymouth and back. Also, following the closure of Southampton Terminus Station
Southampton Terminus railway station
Southampton Terminus railway station served the docks and city centre of Southampton, England. The station was first authorized on the 25 July 1834, it began as the terminus of the London and South Western Railway...
, the section of non-electrified track served Ocean Terminal exclusively - a failure here would not inconvenience other services - the same was not true West of Bournemouth. The steep ascent from Weymouth would also have taxed their 650 HP diesel output to the utmost, as the 'Channel Islands Boat Train' usually loaded to 11 cars.
Class 73 had a simpler electrical system arrangement for control of the dual power sources - even to the point of two separate power controllers on the driver's desk; one for diesel and one for electric. The complex control system of Class 74 (with one dual-purpose controller) was problematic and the class was dogged with electrical system failures up to their last days. Together, the three complaints of poor reliability, difficult engine starting and excessive noise made Class 74 unpopular with crew and fitters alike.
When in good order they were sprightly performers and running on third rail with the full 2552 hp brought to bear (the original class 71 traction equipment having been down-rated slightly from 2700 hp to extend service intervals), many runs in excess of 100 miles per hour (160.9 km/h) were noted despite a stated maximum of 90 miles per hour (144.8 km/h) - though nothing approaching this was achievable on diesel power. Their electronic power delivery meant that acceleration was equally impressive on both diesel and electric power sources. Running on the diesel engine however, available power was pretty much exhausted by the time 60 miles per hour (96.6 km/h) or 70 miles per hour (112.7 km/h) was reached with 'normal' loads and heavy loads (even 8 or nine loaded milk tanks over the banks of the West London Line) would tax them. Speeds would drop and recovery margins in timings taken full advantage of.
They were regular visitors to the London area, often running on Midland
London Midland Region of British Railways
The London Midland Region was one of the six regions created on the formation of the nationalised British Railways and consisted of ex-London, Midland and Scottish Railway lines in England and Wales. The region was managed first from buildings adjacent to Euston Station and later from Stanier...
and Western Region
Western Region of British Railways
The Western Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992...
tracks. In the early half of the 1970s, milk trains for the Southern Region were a staple for the class as far as Acton Yard, requiring diesel power from Clapham Junction
Clapham Junction railway station
Clapham Junction railway station is near St John's Hill in the south-west of Battersea in the London Borough of Wandsworth. Although it is in Battersea, the area around the station is commonly identified as Clapham Junction....
through Kensington and onto the Western Region mainline (Class 52
British Rail Class 52
British Rail assigned Class 52 to the class of 74 large Type 4 diesel-hydraulic locomotives built for the Western Region of British Railways between 1961 and 1964...
or occasionally Class 47
British Rail Class 47
The British Rail Class 47, is a class of British railway diesel-electric locomotive that was developed in the 1960s by Brush Traction. A total of 512 Class 47s were built at Crewe Works and Brush's Falcon Works, Loughborough between 1962 and 1968, which made them the most numerous class of British...
were used for the major haul west of Acton to and from Cornwall and Devon). This would usually produce two trains per weekday and often two different examples of the class. These trains were of note as they often included Diesel Brake Tenders (DBT - basically heavy, weighted bogie wagons with vacuum brakes) to assist with available braking effort.
Although their multiple working abilities allowed them to control (with a single crew) each other, Class 73, EP multiple unit stock and any blue star coded mainline diesel locomotive, multiple operations were exceptionally rare. Wherever Class 74 was noted with another locomotive, the '74 would invariably be 'dead in-train' - i.e. failed and subsequently rescued. One exception to this were the frequent balancing runs between their home depot of Eastleigh and their day-time out-stations of either Clapham Junction yard or Stewarts Lane depot in readiness for night-time postal and newspaper trains from Waterloo. These were nearly always light-engine or occasionally combined with empty coaching stock (ECS) moves with both locomotives under power - over 5000 hp.
The entire class was allocated to Eastleigh
Eastleigh
Eastleigh is a railway town in Hampshire, England, and the main town in the Eastleigh borough which is part of Southampton Urban Area. The town lies between Southampton and Winchester, and is part of the South Hampshire conurbation...
depot for their operational life and 74003 was the last locomotive to enter Eastleigh works for repairs. In common with Class 73, Class 74 was sent to Crewe
Crewe Electric TMD
Crewe Electric TMD is an AC electric locomotive Traction Maintenance Depot situated to the north of Crewe railway station. The depot is situated on the south side of the Crewe to Chester railway line opposite Crewe Works on Victoria Avenue. The depot is operated by EWS...
for heavy maintenance up until 1972, when Eastleigh took over all treatment of both classes.
The end
In 1976, the first example was withdrawn: 74006 (erstwhile E6106) was damaged by fire and beyond economical repair.Although at this time, the electronic control problems of the class could have been resolved (by virtue of the evolution of electronics) and British Rail had demonstrated a willingness to undertake heavy re-design work on other locomotive types to improve reliability (notably on Classes 82
British Rail Class 82
The British Rail Class 82 electric locomotives were built by Beyer, Peacock and Company between 1960 and 1962 as part of the West Coast Main Line electrification.- History :...
, 83
British Rail Class 83
The British Rail Class 83 electric locomotives were built by English Electric at Vulcan Foundry, Newton-le-Willows as part of the West Coast Main Line electrification.- History :...
& 84
British Rail Class 84
The British Rail Class 84 was a 25 kV AC electric locomotive that operated on the West Coast Main Line of the London Midland Region.- History :...
) the work for which the class had been built was drying up. Boat trains were greatly reduced in number and many of the remaining were replaced with multiple units. Freight and parcel work was contracting and Class 74 was embarrassingly short of work (as was the progenitor Class 71), due purely to the changing tides and fortunes of the railway business. In July 1977, 74002 was withdrawn following a collision and a month later, 74009 failed and budgetary permission to repair was not forthcoming. On the last day of 1977 the seven remaining members of class 74 (and all 14 members of Class 71) were withdrawn from traffic. They languished at Eastleigh depot for almost a year until all but 74010 were stripped of reusable components and dispatched to various scrap yards. 74004 & 74009 remained at Long Marston
Long Marston, Warwickshire
Long Marston is a village about southwest of Stratford-upon-Avon in Warwickshire, England. The southern and western boundaries of the parish also form part of the county boundary with Worcestershire.-History:...
until August 1978 whence they were reduced to scrap. 74005 was the last surviving member of the class being finally broken-up in January 1981 at Fratton near Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...
not far from its home depot.
Departmental use
As other members of the class were being put to the cutters torch, Eastleigh performed a light overhaul on 74010 and returned it to fully servicable condition. In 1978, it was towed to DerbyDerby
Derby , is a city and unitary authority in the East Midlands region of England. It lies upon the banks of the River Derwent and is located in the south of the ceremonial county of Derbyshire. In the 2001 census, the population of the city was 233,700, whilst that of the Derby Urban Area was 229,407...
depot for evaluation as a potential candidate for departmental use at the Railway Technical Centre
Railway Technical Centre
The Railway Technical Centre in London Road, Derby, UK, was built by the British Railways Board in the early 1960s to be its technical headquarters....
and remained in the depot yard for some time. Despite being in fully working order with a mass of spares available (from sister locomotives now scrapped) it was eventually deemed unsuitable, towed to Doncaster
Doncaster
Doncaster is a town in South Yorkshire, England, and the principal settlement of the Metropolitan Borough of Doncaster. The town is about from Sheffield and is popularly referred to as "Donny"...
and scrapped in 1979.
| Type HB | Previous Type HA | TOPS | Disposition |
|---|---|---|---|
| E6101 | E5015 | 74001 | Scrapped |
| E6102 | E5016 | 74002 | Scrapped |
| E6103 | E5006 | 74003 | Scrapped |
| E6104 | E5024 | 74004 | Scrapped |
| E6105 | E5019 | 74005 | Scrapped |
| E6106 | E5023 | 74006 | Scrapped |
| E6107 | E5003 | 74007 | Scrapped |
| E6108 | E5005 | 74008 | Scrapped |
| E6109 | E5017 | 74009 | Scrapped |
| E6110 | E5021 | 74010 | Departmental then scrapped |