Dm3

Designed to haul iron ore trains of weight in excess of 5000t over the 1 in 100 (1%) grades of the Lucea - Narvik corridor; the Dm3 was for many years the world's most powerful electric locomotive.

Based on the simple but succesful locomotive designs of the 1920's; the Class Dm ("m" for malm or iron) were virtually 2 single ended Class D units coupled back to back, and having one trailing axle on each replaced by coupled drivers.

Introduced in the 1940's, these double headed monsters began to work the tricky iron ore line; along with 4 units owned by the Norwegian State Railways (NSB class el 12). The popularity and survival of the Rod-Drive design at these lattitudes could perhaps be attributed to it's effectiveness as a method of controlling slip on individual pairs of wheels; amid the polar temperatures of the Arctic circle.

By 1960 it was apparent that greater power was required, and SJ opted for cabless units without pantographs, that were placed in service between the vehicles of Dm Class pairs. The resulting Dm3 Class developed a whopping output of 9,600hp. The high tractive effort of over 900kN resulted in excessive strain on standard screw couplers; and accordingly SJ embarked on a programme of replacing them with Russian pattern automatic couplers.

Resources

General Data

Gallery - European Railway Server
Swedish Electrics - Svenska Elloc (in Swedish)
Swedish Trains - Lokstallet/The Roundhouse

Many thanks to Fredrik Skog.