Partial discharge testing is the most favored non-destructive experimental method for the assessment of the high voltage systems' insulation performance and quality. Therefore, measurement of partial discharges has an important role in high voltage industry. Partial discharge measurements of high voltage devices are performed with sinusoidal voltages in laboratory conditions. However, high voltage systems are exposed to different stresses caused by harmonics, during operation. In this study, the effects of voltages distorted with harmonics on partial discharges are observed experimentally. In experiments, the point-hemisphere electrode system was used and, its partial discharge behaviour was analyzed at sinusoidal voltages and at voltages containing one of the third and fifth harmonic components. The obtained data were analyzed using a phase resolved partial discharge measurement system which was developed within the scope of the study. The experimental results show that the test voltages containing harmonic components may cause errors on the measurement results. It is concluded that the average number of occurred pulses during discharges should be considered in conjunction with the measured apparent charge.