The SNCF Class BB 900 was a class of 35 mixed-traffic electric locomotives built between 1936 and 1937 for État. The class was a development of the pre-war Midi Class E4700 and very similar to the later Class BB 300 and Class BB 325. Initial use was on the Paris–Le Mans line. The class was withdrawn in 1987 after 50 years in service.

History Context In the early 1930s, the economic crisis hit and the government undertook major works to support employment, known as the Marquet plan. It was in this context that the decision was made to electrify the line from Paris-Montparnasse to Brest, between Paris and Le Mans. In anticipation of the completion of this work, the State company ordered two series of electric locomotives: the Class 2D2 5400 for the passenger services and the BB 900 for freight trains.

The BB 900 were a development of the Midi E 4200 and E 4700 classes. The Midi company had a long experience in electric traction and the BB Midi were very successful. Compared to their predecessors, the new locomotives had different gear ratios, the profile of the line being less hilly than that of the lines of the South. Likewise, they were not fitted with rheostatic braking, being less useful on the plain.

Service The class was ordered by État from Alsthom in 1934. The class was originally numbered BB 101–BB 135. Upon delivery, from 1936 to 1937, the class was assigned to the Montrouge depot. Their main duties were operating heavy freight services on the newly electrified Paris-Le Mans line. Some passenger trains are also operated by these locomotives, at the head of Talbot trainsets. A BB 900 at the head of a train could match the running of a Somua Z 3800 railcar. During the tests a speed of would have been sustained.

One locomotive was a casualty of the Second World War. BB 125 was destroyed in July 1944 in the air attack on the Maintenon viaduct by the USAAF.

In the SNCF renumbering scheme of 1950, the class was renumbering BB 901–BB 935, omitting BB 925.

During the 1960s the class underwent major overhauls. Shortly after, some members of the class were transferred to the depot in Limoges, with the remainder following around 1975.

The modernisation of the SNCF electric fleet entailed the gradual withdrawal of the class from 1982 to 1987.

Technology The technology used was the same as that proven on the Midi machines, with an increase in power compared to the BB 4700. As with their predecessors, the bogies are linked together and include shock devices.

The body was made of welded steel, integrated with the frame. It had two driving cabins. The traction motors were nose suspended: on one side, the motor rests on the central cross member of the bogie supported by helical springs, on the other side it rests on the axle to be driven. The engine/bogie transmission is bilateral, as with all the other BB Midi, with a ratio of 3.273.

Regarding the electrical part, the 4 motors are of the M1E type and had a one-hour rating of at 1500 V. They could be connected in series, series-parallel (2 by 2), parallel. Unlike the Midi BB 4700, these locomotives did not have rheostatic electric braking which was deemed unnecessary on the Paris - Le Mans line.

The motors were controlled by means of a 29-notch controller, wired as follows: 0: open circuit 1 to 10: series operation, on starting resistors 11: direct series operation 12 to 18: series-parallel, on resistors 19: direct series-parallel 20 to 27: parallel, on resistors 28: full field parallel In addition to this controller, the driver also had a shunt lever with 6 positions allowing "reduced field" operation and a direction switch. The current collection was by two Faiveley pantographs. The high voltage circuit consisted of a double disconnect switch and a circuit breaker. The motors were coupled via a battery of electro-pneumatic contactors.

During the general overhaul, the end doors were removed and the engine control and electrical wiring completely refurbished.

Fleet list État number SNCF number In service WithdrawnBB 101 BB 9011 January 193627 April 1984BB 102 BB 9021 October 193626 June 1984BB 103 BB 9031 January 193722 January 1985BB 104 BB 9041 January 1936January 1982BB 105 BB 9059 December 1937December 1983BB 106 BB 9061 October 1936December 1983BB 107 BB 9073 October 1936January 1982BB 108 BB 90810 October 193628 February 1987BB 109 BB 9091 January 193628 February 1987BB 110 BB 91026 October 1936January 1982BB 111 BB 9111 January 19367 January 1985BB 112 BB 91221 July 193712 September 1984BB 113 BB 91313 July 1937January 1982BB 114 BB 91427 April 193631 May 1985BB 115 BB 9156 July 19375 March 1987BB 116 BB 9166 July 193730 August 1985BB 117 BB 9173 July 1937January 1982BB 118 BB 9181 January 1937December 1983BB 119 BB 9191 January 1937January 1982BB 120 BB 9201 January 193716 April 1985BB 121 BB 9211 January 1937December 1983BB 122 BB 9221 January 1937December 1983BB 123 BB 9231 January 193730 May 1984BB 124 BB 9241 January 19373 April 1987BB 125 1 January 193725 July 1944BB 126 BB 9261 January 193728 February 1987BB 127 BB 9271 June 193719 March 1984BB 128 BB 92810 August 193728 February 1987BB 129 BB 9291 January 193728 February 1987BB 130 BB 9305 August 193719 March 1984BB 131 BB 9311 January 1937January 1982BB 132 BB 9321 January 193714 June 1985BB 133 BB 9334 August 1937December 1983BB 134 BB 93429 July 1937December 1983BB 135 BB 93513 October 1937January 1982

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