Diesel-electric locomotive wheel slipping; causes, effects, and methods of control

WHEEL slipping is a serious problem in Diesel-electric locomotives. At best, it results in loss of tractive effort which is the locomotive's only reason for existence. On the other hand, slipping can result in mild to extensive damage to traction motors, rails, and main generators. The Diesel-electric locomotive has an electric transmission capable of converting the constant horsepower output of a Diesel engine into a widely variable tractive effort-speed characteristic. This characteristic (within design limitations and ignoring relatively minor variables such as generator, motor and gear losses) is, theoretically, an equilateral hyperbola with the axes as asymptotes. There are practical limitations at both ends of the curve as to how much of the curve may be utilized, and both limits are important to this discussion. At the slow-speed high-tractive effort end, limits of rail adhesion are encountered, while at the high-speed low-tractive effort end the traction motors have an unfortunate tendency to come apart.