Given specific performance curves for a diesel engine, main alternator, and traction motors, outline the methodology to calculate the overall powertrain efficiency of a diesel-electric locomotive under varying load conditions, including losses at each stage.

To calculate the overall powertrain efficiency of a diesel-electric locomotive under varying load conditions, a sequential energy conversion analysis is performed from fuel input to mechanical power output at the rails, accounting for losses at each stage. Overall powertrain efficiency is defined as the ratio of the useful mechanical power delivered to the rails (or drawbar) to the chemical energy input from the fuel consumed by the diesel engine.