Purpose. The results of the electric field intensity measurement within one span of the 330 kV extra-high voltage overhead power line were analyzed. The effect of vegetation on the distribution of the electric field near the overhead power line was examined. Methodology. To measure the electric field of an overhead power line, a metering device, designed to measure the root-mean-square value of the intensity of an alternating electric field varying with a 50 Hz frequency was chosen. In the electric field measuring device, three transducers are used, oriented in three mutually perpendicular directions. Equivalent charge method was used to estimate the maximum value of the electric field intensity in the middle of the span of overhead power line. Results. Experimental data show that on the right side of the transmission line route, where a row of deciduous trees grow, the electric field intensity is 31.2 % to 55.2 % lower than on the left side, where there are no trees. The values of the electric field intensity calculated accounting overhead shield wires are 3.4 % lower than without them. The experimental data are in good agreement with the calculations by equivalent charge method. Originality. Considered overhead power line with a horizontal arrangement of wires is symmetrical about middle phase and therefore it facilitates the analysis of the influence of ground objects on the distortion of the electric field distribution, specifically, deciduous trees located only on the one side of the line route. Practical value. Deciduous trees planted in a single row have a shielding effect, limiting the electric field intensity at a height corresponding to the average height of a human being. Conclusions. With an increase in the area of deciduous tree growth outside the edge of the transmission line right-of-way, the decrease in the electric field strength will be more significant. Future efforts should be focused on environmental impacts of extra-high voltage and ultra-high voltage overhead power lines as well as lightning performance of such lines. References 10, figures 8.

Purpose. The global development of high-voltage direct current transmission has led to a growing interest in partial discharge measurement and analysis at direct current voltage. Partial discharge measurements in dry and moistened insulation under alternating and direct current voltages were performed. Methodology. Technique of electrical detection of partial discharges was applied. Measuring system when coupling device is connected in series with the test object was used. Results. The impact of partial discharges, mainly corona discharge, on the environment was reviewed. The effect of insulation wetting on the characteristics of partial discharges at various voltage waveforms was studied. Under a direct current voltage conditions, a removal of absorbed moisture as influencing factor leads to the almost complete elimination of partial discharges and a decrease in their amplitude by more than 90% compared to moistened sample. Originality. Modified measuring system allows partial discharge measurement at various voltage waveforms. Partial discharge measurements at alternating and direct current voltages were carried out under the same conditions, including the same magnitude of applied voltage and moisture content in the insulation. The applied voltage varied from 7.3 kV to 9.0 kV. The moisture content in the insulation varied from 2.0% to 12.0%. The main attention is paid to the effect of voltage ripples on the characteristics of partial discharges. Practical value. The data obtained contribute to the study of the partial discharges phenomenon when the insulation is exposed to non-standard waveforms of applied voltage. Conclusions. Phase-resolved partial discharge analysis can be used for a ripple voltage waveform too. The required phase angle assignment to a single partial discharge event becomes possible due to the ripple peaks being present in the rectified voltage oscillogram. Future efforts for this research should be focused on specific questions regarding application of three-capacitance model for simulation of partial discharges under ripple voltage conditions and study of environmental aspects. References 19, figures 7.