Purpose: As electric locomotives work in changing load conditions, the question on how traction drive energetic efficiency indicators depend on being realized capacity has important meaning. The task is set to get in the course of experimental research — energetic efficiency main indicators — efficiency coefficient, capacity usage coefficient and capacity coefficient — of asynchronous traction drive of new freight electric locomotives 2(3)ES5S of “Ataman” family at work with changing load. Methods: Studies are given on full-size bench for traction drive testing. Special attention is paid on experimental definition of losses depending on being realized capacity. The bench’s built according to mutual load scheme, each of two channels includes traction converter and wheel-drive block. Wheelset axles of two wheel-drive blocks are connected with the help of torque clutch which allows to register torque values on wheelsets and rotation frequency. Results: Tests are hold for capacity six levels that has made it possible to obtain dependencies of efficiency coefficients of drive main elements versus changing load. The results are shown in tabular and graphical forms. It’s also shown how efficiency coefficient does change depending on load (according to board logger). Practical significance: The obtained dependencies of efficiency coefficients of drive main elements (converter and traction electric drive with reducer) from load value represent initial information for the work of the algorithm of discrete-adaptive control of multidrive traction gear which’s applied on electric locomotive 2(3)ES5S. This algorithm realization has allowed to cut specific expenditure of electric energy on traction in 20–30% limits depending on exploitation conditions.