NSB Di 6, later designated ME 26 and DE 2700, is a class of twelve diesel-electric locomotives built by Siemens for the Norwegian State Railways (NSB). The prime mover provides a power output of , a starting traction effort of and a maximum speed of . They have a Co′Co′ wheel arrangement. The bidirectional locomotives were designed for use with both passenger and freight trains.
The units were ordered by NSB in 1992 as replacements for the aging Di 3, and were particularly intended for use on the Nordland Line and to a lesser extent on the Røros Line. Construction was done by Maschinenbau Kiel (MaK) in Kiel, Germany, which was then part of Siemens Schienenfahrzeugtechnik. The class is largely based on the MaK-built DB Class 240, with each unit costing 32 million Norwegian krone (NOK). The first units were delivered in March 1996, one year after schedule, but were plagued with faults. By 1999, the entire order was terminated and the locomotives returned to Germany. They were taken over by locomotive lessor Dispolok and were used by various Germany railway companies. Ownership was taken over by Vossloh in 2003, after which most of the class were leased to German passenger train operator Nord-Ostsee-Bahn. In 2008, three units returned to Norway and are used by Cargolink for freight trains.
History
During the late 1980s, the Norwegian State Railways sought a new locomotive type to replace its aging fleet of Di 3 diesel-electric locomotives, which made up the back-bone of the dieselized operations. The new locomotives were planned for use as freight and passenger trains on the Nordland Line, and to a lesser extent on the Røros Line. In 1980, NSB had taken delivery of five Di 4 from Henschel. Originally there were plans to order additional Di 4 units, but this was discarded and instead a new class was pursued, as NSB wanted similar, but slightly more modern, locomotives.
A MaK-built DB Class 240 locomotive was test-run in Norway during 1990. On 23 November 1992, NSB's board decided to order ten similar units. The order was later expanded with another two units because NSB was offered a lower price than originally stipulated. The Di 6 would have motors from Siemens, who had bought MaK, and would be optimized for Norwegian conditions and standards. The contract was worth NOK 380 million, or NOK 32 million per unit. At the same time, NSB also made an order for 20 smaller diesel-electric locomotives from MaK, the Di 8. Between the two new classes, they were to replace all the Di 3s.
The contract for the Di 6 called for the first delivery in February 1995. Several components were to be manufactured by NSB, including the fuel tanks, sandboxes, engine frames, alternators and some components for the bogies. The first locomotive was delivered on 7 March 1996, but quickly proved to not meet the specifications in the contract. In particular, the locomotives had too high fuel consumption and the bogies had faults, as they had too high track forces. Both of these issues were difficult to solve. The Di 6 also had problems with overheating, in particular in the main alternators, the oil cooler and the brakes. The on-board computer failed when the outdoor temperature fell too low.
On 23 September 1996, NSB's administration recommended that the purchase be terminated. However, this was put on hold by the board. Instead, a renegotiated contract was signed, whereby Siemens was obliged to deliver the locomotives, as specified, by mid-1997. If not, the two parties agreed that the contract would be terminated. By late 1996, five locomotives had been delivered, and these were returned to Kiel for upgrades. The first returned to Norway on 30 November 1996, after the ventilator motors had been upgraded, new oil coolers installed and other minor upgrades had been performed. From January 1997, they were put into regular use with freight trains on the Nordland Line. In mid-1997, number 664 was damaged in a fire caused by an incorrectly mounted exhaust system. In October 1997, cracks were found in the wheels, and all units were taken out of service while they were being fixed.