The Renfe Series 251 is derived from the Japanese National Railways (JNR) EF66 series. The units that make up this series were received between 1982 and 1984. The first two locomotives built by Mitsubishi Electric Corporation (MELCO) in Japan arrived at the port of Barcelona on 30 April 1982 aboard a ship called 'Sweet Flag'. After passing through Can Tunis, they were taken to Beasain (Gipuzkoa) for servicing and to begin trials at the mountain passes of Pajares and Despeñaperros. The rest of the series was built in Spain by Construcciones y Auxiliar de Ferrocarriles (CAF) and Material y Construcciones S.A. (MACOSA). WESA and General Eléctrica Española (GEE) also played a part in this.
The last locomotive manufactured by MACOSA (251.029-5) went into service on 2 March 1984. Interestingly, the last of the series (251.030-0, manufactured by CAF) had already been in service for almost a year on 27 May 1983).
Construction was divided as follows:
The 251 series locomotives are aesthetically inspired by the Japanese National Railways JNR66 series, from which they are derived technically. However, the 251 box does not have the characteristic indent halfway up the box that Japanese engines do, due to the more restrictive, 1-yard gauge of the track, so the grids go higher up.
The side grilles on the first two locomotives in this series, built by Mitsubishi, were painted blue, while the remainder had silver grilles. They were then put in the 251.002, with the 251.001 keeping the original colours while they were being held at the Central Repair Workshop in Villaverde Bajo (Madrid). On 17 October 1984, this locomotive towed the train that transported the King and Queen of Spain to Pajares for the line's 100th anniversary. It was set aside in 1995 to be used for spare parts for the rest of the series, decommissioned in July 1999, and later scrapped.
Once the locomotives were received, and before they were put into regular service, tuning and approval tests had to be carried out. These tests included attaching a 251 locomotive to a train with the Renfe 277 Series locomotive it owned, bringing the towed mass to around 650 mt. The Busdongo - Pola de la Lena route was taken to test the electric brake, among other parameters, and went back up to Busdongo to continue the test. Other tests including checking tensile stress, wheelslip and maximum t-loads that could tow on a gradient of 20-thousandths. One of these tests was with the 251-001 in the mountain pass of Pajares, where the locomotive managed to tow a train of no less than 1300 t, albeit at a speed lower than 50 km/h. Subsequently, no. 4 tested on the Despeña perros line, having some problem with the 50 Hz detector (automatism that detects the voltage of the catenary) since the voltage must be exclusively 3,000 Volts in continuous c.
In the early 1990s, The Business Units (BU) appeared in RENFE. All the locomotives from the 251 series were assigned to the Traction BU, so they were painted with the corporate colours (yellow and dark grey), already tested in the 269-604-5 (Gato Montés). Thus began the pictorial standardisation of the entire engine fleet, with the previous chromatic variety disappearing from the railway landscapes: express with blue sleeper carriages, green 8000 carriages and "Estrella", |yellow Correos carriages... In 1994 the Traction BU began a process to specialise its locomotives, involving the assignment of its fleet to specific services. The entire 251 series was assigned to the Freight Business Unit, and the locomotives incorporated a sticker on the side with the logo of this Business Unit, a UN in which they remain today (2010), renamed Renfe Mercancías (Renfe Freight), when merged with Combined Transport. The top speed was limited from 160 to 140 km/h in passenger service due to various stability problems with the central bogie as well as mechanical issues with the bi-transducer transmissions.
While undergoing checks at the Central Repair Shop in Villaverde Bajo, the longitudinal plates that served as decoration on the front were removed, since water stagnated in these parts and created corrosion problems. Once the area was cleaned, it was painted yellow and the RENFE logo was added.
Over the years, other tweaks have been made to these locomotives: removing the numbering and embossed decoration on the end carriages, installing dual optic lights (some using the original housing and others with new housing), Train-Ground antenna (only in cabin 1).
It has a B'B'B' set of wheels with a dual motor bogie, Mitsubishi model MB-3200-B3 induced (practically the same as that equipped in the 269 and 289) with a total maximum power of 4650 kW, 1550 kW per bogie motor. The maximum weight of 138 tons. Traction control is carried out by a chopper device, equal to that of the |269,600 (this is the first series of RENFE locomotives fully equipped with this electrical equipment), and each engine has two independent "choppers" that deal with its regulation. The first is biphasic and regulates the motor voltage, the second is single-phase and regulates the degree of "shunting" of the motor. The rheostatic electric brake has independent excitation from the traction and forced ventilation chopper. A feature of chopper-regulated locomotives is that the connected engines are in parallel. All auxiliary service motors such as the traction motor fan, brake resistors, electronic control blocks as well as air compressor and vacuum pumps are powered by 380 V three-phase alternating current produced by two motor-alternator groups, the battery voltage is 72 V. The bogies are identical to those of the 269, 279 and 289 series. They are also bi-gearors, so they can work with two stress curves according to the needs that correspond to the maximum speeds of 100 (PV, freight) and 160 km/h (GV, passengers). The central bogie has a roller device in the body-bogie junction that allows the necessary transverse movement of the bogie around bends. With no pivots or bogie bolster, the body rests on the helical springs so characteristic of these machines that, in addition to withstanding the loads, allow the rotation and transverse movements between bogie and body, constituting the secondary suspension because the primary is based on helical springs of each grease box.
There are 3 types of brakes used on the 251: Electrical-rheostatic that, in addition to being used to retain the locomotive, is combined with the compressed air brake, the compressed air pneumatic brakes for the locomotive (independent) and the compositions of the trains, and the vacuum brake compositions of trains that have this type of braking. Both the vacuum pump and the compressor are powered by 18.5 kW power electric motors.
The ceilings, like the body, are divided into three sections with removable panels that facilitate access to the equipment they contain for maintenance. In the central section are the three braking resistance blocks with forced ventilation, as well as the three ten-resistance fans that produce a very characteristic sound when the dynamic brake comes into operation and that gives it away when approaching when driving in line.
On the front is the 100 t traction hitch on rubber springs, and stops, both of which are mounted on a detachable headboard which protects the chassis in case of impact by deforming the spring and absorbing such shocks.