Electrical insulation materials quality and reliability play a central role in providing the electrical machines reliable operation. It is well recognized that insulating system of low voltage motor fed by converter is exposed to electrical stresses arising from repetitive square waveform of supplying voltage while additional impact of temperature, vibrations and environmental operation conditions are imposed. The implementation of wide bandgap power semiconductors as SiC and GaN in recent years allows to create very powerful converters with high switching speed. On the other hand it leads to a remarkable increasing electro-thermal constraints applied to windings' turn-to-turn insulation of motors fed by such converters. The relevance of new testing methods and test benches is well found by remarkable modern advances in semiconductors technology. Testing methods for low voltage motors winding wires insulation proposed in this paper permit to evaluate the withstand capability of insulation materials applying the high frequency modulated signals representative for traditional converters supplying (μs level of impulse rise/fall time), as well as the voltage waveforms with very straight adjustable dV/dt, very fast rise time and fall time (ns level of impulse rise/fall time) engendered by new semiconductor devices based on wide bandgap materials. The possibility to modify experiment parameters in wide rage for insulation endurance tests allows to obtain a rich data for further analysis.