Repetitive transient aging, the influence of rise time

Power electronic devices are becoming very popular as they are linked with renewable energy sources. Their primary use is to switch between DC and AC waveforms so that the energy generated at locations such as wind farms and solar plants can be used by the power grid. Although cheap and reliable, power electronic converters generate repetitive transients that affect HV components such as transformers and cables. The three main features of these transients, repetition frequency, rise time and magnitude are the cause of premature failure in the insulation system of HV devices. Rise time is responsible for the energy injected into the paper insulation as it determines the speed at which cellulose fibers are polarized. This causes movement at a molecular level which weakens the insulation. Increasing the speed at which the transient reaches its maximum level causes bigger damages to the insulation. Polarity also has an effect. Results are presented in this contribution when transients of different rise time are applied to oil impregnated cellulose.