Increasing DC-link voltages and high inverter slew rates in electrical traction drives may be a serious risk for conventionally designed insulation systems. Resulting overvoltages can cause partial discharges (PD) if the critical voltage inside the insulation system is exceeded. This applies in particular to the winding insulation, which is predicted to be the weakest point. The critical voltage can be determined using the Paschen curve. The partial discharge inception voltage (PDIV) is not only depending on the amplitude of the electric field but also on the timely sequence. Modeling partial discharge processes is an instrument to predict the electrical load on insulation systems and to evaluate possible new design criteria for insulation systems. The presented model uses the volume-time-theory to calculate the PDIV of twisted pairs of enameled wires. The results of the simulation are compared to PDIV measurements for bipolar voltage pulses with short rise times.