Harmonic Currents Generated by MV Modular Converters and Thermal Insulation Aging of Polymeric Cables

Electrified transportation relies broadly upon power electronics to optimize power supply, in a framework of power density, efficiency and load dynamics maximization. If, on one side such, goals can be achieved thanks to the rapid increase of power electronic component reliability, voltage, slew rate, modulation frequency, on the other hand all of this can have negative impact on electro-thermal insulation life. Accelerated aging processes, not expected and accounted in insulation design based on AC sinusoidal electrical stress experience, have to be analyzed and modelled to design properly electrical insulation and ensure its long-term reliability. This paper focuses on the contribution of harmonic-current losses on thermal aging of electrical insulation of cables connected to MV modular converters. Calculations and simulations show that losses, even if higher on the AC side as compared to the DC side, are not large enough, if the converter design is done properly, to significantly affect thermal life, in both XLPE and EPR insulated cables. This outcome can be reversed in case of poor design, not considering specifically dielectric losses and heat dissipation.