The inverter supply of asynchronous induction machines for traction applications has a major influence on both electromagnetic and thermal performance. In addition asynchronous induction machines used with traction drives of rail transportation vehicles have different design strategies compared against commonly used standard machines. Generally, the design of these machines requires high electromagnetic and thermal stress. Thus, the additional losses caused by the inverter have to be considered with the initial design. Concerning the thermal design, a precalculation of the additional losses at various operating points is necessary. The additional losses depend on the characteristics of the machine as well as on the operating mode of the inverter. DC-link voltage and switching frequency have major effects on the additional losses. An important viewpoint of modelling and precalculation presented herein is given to the comparison with detailed measurements from different already built machines. Furthermore, the precalculation of additional losses enables the determination of an optimized switching mode to minimize the losses in the system of inverter and induction machine.