Studies of partial discharges at sinusoidal, non-sinusoidal and impulse voltages

Progress and modern demands set for the design of electrical insulation systems, working at specific non-sinusoidal voltages, need for new investigations in the area of partial discharge (PD) inception and development. Working conditions and in-service stresses, i.e. non-sinusoidal voltages, overvoltages, harmonics and pulse-width-modulated type voltages have crucial influence on arising of PD in insulation systems. Their influence on partial discharge development differs from influence in normal conditions at nominal sinusoidal voltage. In such a case analysis and 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 on partial discharge pulses, their statistical parameters and changes with increasing of applied voltage. Presented results of measurements made for sinusoidal, triangular and trapezoidal voltages show differences having source in PD mechanism. Slew-rate of applied voltage and peak voltage value determine specific conditions for PD generation and have important consequences for phase location of discharges.