Analysis of conditions of partial discharges inception and development at non-sinusoidal testing voltages

Progress in construction of electrical insulation systems needs new investigations of partial discharges (PD) mechanisms. Working conditions and exploitation stresses, i.e. overvoltages, harmonics and other disturbances have crucial influence on arising of PD in insulation systems. Their influence on partial discharge development is different from normal conditions at nominal sinusoidal voltage. In such a cases interpretation of measurement results (by classical or phase-resolved PD images method) could be more difficult. Paper presents influence of sinusoidal and non-sinusoidal testing voltages (triangular and trapezoidal) on partial discharge distributions, their parameters and changes with increasing of applied voltage. The test object was real insulation system (stator bar thermo-setting insulation system) with many internal PD sources. Presented results of measurements made for sinusoidal, triangular and trapezoidal voltages show the PD mechanism in these conditions. Slew-rate of applied voltage with fixed peak voltage value determines specific conditions for PD generation and has important consequences for phase location of discharges.