The Three-Phase Current Pioneer.
The class 120 marked the technological change to three-phase current propulsion. This principle promised compact motors without commutators and largely free of parts that would wear out, commutator rings, brushes, and mechanical contacts. The performance specifications for this new development were broadly formulated as a wish list, because a wide torque range and rpm range can be mastered with three-phase current technology. The class 120 was designed to pull InterCity trains at speeds of 200 km/h / 125 mph and 5,400 metric ton freight trains, and be equipped with push/pull controls and electric regenerative brakes. In 1977, the DB ordered five experimental units, which were thoroughly tested on test stands, on test runs, and in operational use. Startup, tractive effort, acceleration, running characteristics, braking power, power consumption, and stability were part of the program. Comparison tests with other makes of locomotives as well as startup tests on the Lötschberg and Semmering grades confirmed the effectiveness of the technology. The speed record was 265 km/h / 165 mph. During the test phase, new developments were introduced, for example: microprocessors for faster monitoring and control. Components were constantly improved until all five units were technically at the same level in 1982 and were ready for regular production. During the several years of development, the purchasing policy changed, however. Instead of all-round locomotives, special locomotives were once again preferred on the basis of common development platforms with many parts in common. Therefore, only the first production run of 60 units were purchased of the class 120. The five prototypes continue to be used for test purposes, and the regular production units are still proving themselves in daily railroad operations.