Electrical stress suffered by medium voltage medium frequency transformer

Medium voltage medium frequency transformers may face electrical stress different from that of conventional transformers. Working under PWM-like voltages, inter-Turn and inter-layer overvoltage could be induced within the transformer's winding. This overvoltage can increase the probability of partial discharge that can degrade the insulation quickly and lead to premature breakdown. Therefore, an investigation on the electrical stress of medium-frequency transformer is necessary. This paper chooses a transformer prototype as a case and creates its equivalent circuit. Based on this circuit, transient inter-Turn and inter-layer voltage simulation is conducted under different voltage rise times, relative insulation permittivity and winding structures. The simulation results confirm the existence of interturn and inter-layer overvoltage and reveal the influence of the above-mentioned parameters on the overvoltage.