Partial Discharges Activity within an Internal Void at AC Voltage Disturbed by High Frequency Components

摘要

Frequent use of power electronics in electrical power systems imposes significant impulse and harmonic voltage stresses on various insulation systems. These systems are stressed by very fast and repetitive voltage distortions, which are superimposed on the power frequency voltage. The shape of voltage distortions is usually given by mutual interaction between switching pulses, emitted by power electronics, and passive parameters of power distribution grid. The lifetime of an insulation system is influenced by partial discharge activity that is a consequence of long-term stresses or manufacturing imperfections. It has been proven that the intensity of partial discharges significantly depends on the operating voltage waveform. The paper deals with the experimental measurement of partial discharges on the physical model of an internal void in a solid dielectric under above mentioned voltage stress conditions. The designed and realized high voltage test circuit consists of a high voltage test transformer and a high-frequency high voltage transformer, to generate the superposition of power frequency high voltage and harmonics up to 15 kV or impulses with various repetition and oscillation frequencies. Gathered patterns and parameters of partial discharges were analyzed and evaluated to determine whether there exists any influence of higher harmonics content on the lifetime of the insulation system. The presented results show that the presence of high frequency oscillations on power frequency voltage have the direct impact on the partial discharge activity. These findings can be significant for the insulation design and insulation lifetime assessment in the power systems containing power electronic switching devices.