DB Class 120 - the first series-produced three-phase loco

The 120 series was driven by a three-phase asynchronous motor. These motors have a significantly lower weight compared to the single-phase series motor. Furthermore, the three-phase asynchronous motors are characterised by more compact installation dimensions and by lower maintenance requirements. The three-phase motor can also withstand high loads when stationary and has no commutators.

Schon im Jahre 1899 konnte mit fester Spannung und Frequenzen aus zwei- oder dreipoligen Fahrleitungen Drehstrom gewonnen werden. Der für den Antrieb von Schienenfahrzeugen genutzt werden konnte. Durch die Verwendung moderner Halbleitertechnik, konnte ab den 1960er Jahren Drehstrom mittels Frequenzumrichtern in Fahrzeugen erzeugt werden. Durch variable Spannung und Frequenz kann die Motorleistung direkt geregelt werden. Erste Erprobungen mit der Drehstrom-Antriebstechnik in Dieselelektrischen Erprobungsträgern der Reihe DE 2500 von Henschel fanden ab 1971 statt.

The diesel engine and the generator had been removed from locomotive 202 002. Furthermore, the locomotive was permanently coupled to a BDnzf 740.2 control trailer. This control trailer was equipped with a transformer and a current collector. Through this conversion, the control car could supply the locomotive with power and a three-phase electric locomotive could be simulated.

Extremely successful trials were carried out with this team in 1974/1975. It turned out that the desired universal locomotive was technically feasible. This was due to the lower maintenance costs and service life. In this way it was possible in principle to replace all electric locomotives in service at the time and to haul any type of train. DB wanted to achieve this as early as the beginning of the 1950s with the E 10 series. However, this was not possible with the alternating current drive of the time. So it came to the split into express locomotive E 10 and freight locomotive E 40 / E 50. With the prospect of a universally usable locomotive, the development order for the Bo’Bo’ class 120 electric locomotive was placed in 1976. BBC was responsible for the electrics and Krauss-Maffei, Krupp, and Henschel for the vehicle part.

The first small series of three-phase locomotives entered service in 1976 with the Henschel E 1200. This was used in the colliery and port railways of Ruhrkohle AG. The knowledge gained from this small series flowed into the development of the DB Class 120.

In 1984, a total of 60 series locomotives of the class 120 were ordered at a unit price of 5.5 million D-marks. The procurement of the last 24 locomotives was approved by Transport Minister Werner Dollinger in April 1985. The purchase contract stipulated the delivery of 36 locomotives and an option for 24 additional machines. This option for 24 more machines was thus honoured. The total investment for this series was 380 million D-marks. Delivery was to be completed by the end of 1988. One visual difference between the prototype and the series machine is the filler neck for the sand supply containers. On the prototypes, the filler neck is smaller and integrated into the bogie. On the series machines, it is triangular and suspended directly from the frame.

The technical changes were rather minor in comparison. For example, the electric resistance brake was dropped in favour of the regenerative brake, which had proven to be reliable. Furthermore, the electric locomotives received an additional high-voltage filter, which required two additional roof lines. These were retrofitted to the pre-series locomotives. The mechanical weaknesses of the pre-series models of the BR 120.0 were retained in the series. The series-production locomotives could also be approved for up to 200 km/h, based on successful trials with locomotives at 160 km/h and an already approved locomotive at 200 km/h.

On 13rh January 1987, the first series-produced three-phase locomotive 120 103 was handed over to Deutsche Bundesbahn by the industry at the Bundesbahn’s Munich-Freimann repair works. Federal Transport Minister Dollinger and Federal Railway Board Member Reiner Gohlke came to the symbolic handover of the keys. The delivery of the 60 series-production locomotives took until the end of 1989. The vehicles were immediately put into scheduled service. They hauled Intercity and Interregio trains during the day and fast goods trains at night, and did so in a streamlined circulation schedule. The locomotives 120 137 to 120 160 were delivered with a modified gear ratio. This allowed them to obtain a higher tractive effort at higher speeds, but this resulted in a lower tractive effort at a lower speed.

Initially, the DB class 120 vehicles were used on the Hanover-Würzburg high-speed line, more precisely on the tunnel-rich southern section Würzburg-Fulda, which was opened in May 1988. The reason for the deployment was that not enough pressurised vehicles were available for this section. In August 1988, 35 percent of the 120 fleet was not available. The reason for this was the correspondingly high level of damage. From 120 136 onwards, there were problems with the wheel guards. This delayed the commissioning of further vehicles.

In 2007, 37 locomotives were used in three schedules, mainly in intercity traffic. The vehicles were also used to supplement the newly established 200 km/h Munich-Nuremberg Express. The DB Class 120 was used less frequently in freight traffic. The series-produced 120 – 120 110, 158 and 159 first retired from operational service and were used as spare parts donors. They were later returned to operational service due to increased demand.

The DB Class 120 158 continues to be used as a spare parts donor and was z-delivered on 16 June 2010. After a long period of work in Munich, it is now in the Dessau repair works. Here, further parts were taken from the locomotive. In January 2011, 49 locomotives were still in service. At the beginning of 2018, the five locomotives that had been parked in Hamm since 2016 were transferred to Opladen and scrapped. The class 120 has no longer been in service with DB Fernverkehr since July 2020.

DB Systemtechnik sold the 120 153 and 120 160 locomotives at the beginning of 2005. These underwent a general overhaul (IS 703) at the Nuremberg factory. In the process, the machines were given different locomotive numbers. 120 153 was given the number 120 501 and 120 160 the number 120 502. Both locomotives are used with test and measurement trains throughout Germany. In 2006, locomotives were loaned to DB Fernverkehr. They were used by DB Fernverkehr in front of regular trains during the World Cup. 120 502 was sold to DB Netz in 2013 and repainted. From now on, the locomotive 120 502 is on the road in yellow.

Since the beginning of 2016, 120 125 has also belonged to DB Systemtechnik as the third locomotive of the 120 series. Since September 2016, the locomotives 120 501 and 502 have again borne their old locomotive numbers 120 153 and 120 160. On 09 September 2020, the electric locomotive BR 120 153 suffered a high-voltage flashover in the engine room. DB Systemtechnik is using the 120 153 as a spare parts donor for the still active 120 125, which is currently parked in Minden. The 120 160 used by DB Netz was parked after the deadline expired in March 2021.

The 120 series has four separate secondary windings of the main transformer. An oil-cooled traction converter is connected to each secondary winding. The traction converter consists of the following assemblies:

Four-quadrant controller (4q-S)
DC intermediate circuit with suction circuit and support capacitor
Pulse inverter (PWR)

The two motors of a bogie are each supplied by two interconnected traction converters. The single-phase voltage of the secondary side of the transformer is converted into DC voltage by the 4q-S. In the 2800 V intermediate circuit there is a suction circuit tuned to 33 1/3 Hz and a back-up capacitor. The DC link feeds the pulse inverters and thus generates the three-phase alternating current with variable voltage and frequency for the traction motors. The variable voltage is 0 – 2200 V chained and the frequency is 0.4 – 150 Hz.

The timing of the 4q-S is 183 Hz. Furthermore, the 4q-S are each offset by 90°. The asynchronously clocked PWRs have a clock frequency of 200 Hz up to a motor frequency of 20 Hz. In order to avoid beatings in the motor current, synchronised clocking methods are used above 20 Hz. The quite similar construction of the 4q-S and PWR allows for a reverse operating direction. This is used for the electric brake of the locomotive. The PWR can feed the DC link with the three-phase current generated by the motors. The 4q-S then generates the single-phase alternating current, which is fed into the overhead line.

On the roof of the locomotive are two single-arm pantographs of the SBS 90 design. This design is a further development of the standard single-arm pantograph of the SBS 65 design. The SBS 90 can be used for speeds up to 20 km/h, while the SBS 65 may only be used up to 200 km/h. Furthermore, the design was 90 kg lighter than the SBS 65 and had better suspension. This ensured contact even at high speeds. Originally, the 120 series was only intended as a test vehicle. Thus, some things in the vehicle part were done differently than usual. For the first time, the main transformer could be placed under the vehicle floor, thus keeping the engine room clean and tidy. Furthermore, the engine room could be equipped with a straight centre aisle.

The largely lightweight construction of the vehicle part initially caused problems. The large gear wheels and gearboxes were designed to be too light. This resulted in frequent fractures and oil leaks. These problems could be solved by replacing stronger parts. For the bogies, the conventional design with pivots was used. Flexicoll coil springs took over the secondary suspension in the running gears. This allows the bogies to return to the centred position after a curve run. Furthermore, transverse movements of the locomotive body were made possible in this way. The hollow shaft cardan joint drive from BBC transmits the power to the wheels. The mass of the traction motors is cushioned by the bogie.

The 120 series was the first to use a three-phase auxiliary power supply system. In addition to small motors, this also enables the control of the auxiliary power units. The 120s have three auxiliary converters (HBU). These are fed via the auxiliary winding of the main transformer. HBU 1 and 2 each supply the two traction motor fans of the bogie. In addition, they also supply a respective assigned transformer oil cooler fan. The HBU also flexibly controls the motor speed. This is done depending on the cooling requirement.

The third HBU works with a fixed frequency and supplies other auxiliary operations, such as the transformer oil pumps, but also the air compressor. The HBU 3 is briefly shut down when the air compressor is switched on, which enables a smooth start-up. All relevant temperature values are automatically monitored by the locomotive. A traction lock is issued if the limit values are exceeded despite the regulated auxiliary operations.

In addition to the electric brake, the locomotives are equipped with a continuous, indirectly acting, multi-solvent compressed air brake type KE-GPR with a direct additional brake for shunting. As a rule, only the electric brake is effective during braking operation. The air brake is pilot-controlled and is only used if the electric brake fails. Due to the three-phase drive technology, the E-brake can act with full force until almost at a standstill, in contrast to the electric resistance brakes. A so-called “cleaning brake” was subsequently installed, which applies the block brake with 0.25 bar brake cylinder pressure when the electric brake is in operation. This is to roughen the wheel treads. This leads to improved traction and braking traction in bad weather conditions. The installed spring brake serves as a holding brake.

With the class 120.1, the DB unit driver’s cab in pressure-tight design was already used from delivery. This meant that the locomotives could also be used on new-build lines. On the 120.0 series, the driver’s cab was retrofitted accordingly. Pressure-protected interiors are important at high speeds. During train encounters, the outside air is strongly compressed by the trains approaching at high relative speed. In the worst case, this can lead to hearing damage. The vehicles used in particular on lines with tunnels must fulfil pressure protection requirements.

The locomotives have the prescribed safety package consisting of:

safety traction control (Sifa).
Point-based train control (PZB) including line-based train control (LZB 80/180 with PZB 90)
GSM-R train path radio
an automatic driving and braking control system (AFB)
control unit for the electro-pneumatic train brake (ep)
Emergency brake override Nbü-DB via IS (the emergency braked train thus does not come to a stop in the tunnel, but after the tunnel)

The locomotives were retrofitted with computers for the EBuLa electronic timetable. Since delivery, all 120s can be used in double traction as well as for push-pull trains. For use in front of push-pull trains, a time-multiplex push-pull control system was used. The 120s were the only locomotives that were allowed to push driving trailer-led IC trains at up to 200 km/h until the use of the class 101. The pre-series locomotives were also equipped with the conventional push-pull control system. Among other things, this allowed the use of push-pull trains with n-carriages.

Due to technical progress in the field of rail vehicle technology, the class 120 is considered obsolete and prone to breakdowns. Of the five prototypes of the DB class 120 electric locomotive, only 120 003 still exists in the Augsburg Railway Park, 120 004 in the DB Museum Koblenz-Lützel, and 120 005 at the TEV in Weimar. 120 001 was so badly damaged in a serious accident that it was scrapped. 120 002 was initially used as a spare parts donor for its sister machines and was then also scrapped.

On the Stuttgart – Karlsruhe and Stuttgart – Nuremberg routes, the class 120 was used in a small fleet until 2020. The fleet was numerically dominated by the class 101. Part of the 120 fleet included the 120 100-6, 120 111-0, 120 118-5, 120 123-5, 120 133-4, 120 134-2, 120 147-4, 120 148-2, 120 155-7, 120 157-3 and 120 159-9. The last scheduled run was on 05 July 2020 with DB Fernverkehr, as IC 2161 from Stuttgart to Munich. The class 120 was also taken out of service on the Hanse-Express between Hamburg and Rostock.

Whereabouts and stock of the DB series 120 (as of July 2021)

Some vehicles of the 120 series were sold to private railway companies. 120 001 and 120 205 have been in service with Bahnlogistik24 GmbH since July 2019. 120 102 and 120 119 followed at the end of 2020 / beginning of 2021 and 120 120 and 120 127 at the end of March. The locomotives 120 145, 120 154 and 120 204 have been in the inventory of WRS Deutschland GmbH since August 2019.