Abstract
The use of HVDC systems is increasing in number due to technological innovations, increasing power capacity and increasing customer demand. The characteristics of insulation systems under composite DC and LI voltage must be examined and clarified. In this study, firstly, experimental circuits were designed to generate and measure composite DC and LI high voltage using a simulation program. The coupling elements used were chosen according to simulation results. Afterward, experimental circuits were established in the laboratory according to the simulation results of the designed experimental circuit. Then, breakdown voltages under composite DC and LI voltage for less uniform and non-uniform electric fields were measured with four different electrode systems for positive and negative DC voltage pre-stresses with different amplitudes. The 50% breakdown voltage was calculated using the least-squares method. Finally, 3D models were created for the electrode systems used in the experiments using the finite element method. The efficiency factors of electrode systems calculated with the FEM results were correlated with the experimental breakdown voltage results. Thus, the breakdown behavior of air under bipolar and unipolar composite voltages (CV) was investigated. In conclusion, the experimental results showed that very fast polarity change in bipolar CV causes higher electrical stress compared to unipolar CV.
Highlights
Introduction published maps and institutional affilHigh-voltage direct-current (HVDC) systems are quickly being applied for transmission systems day by day
The value of the applied DC voltage pre-stress is positioned along the x-axis, while the value of the composite voltage is positioned along the y-axis
For the breakdown voltage experiments in the non-uniform electric field, two rod electrodes with different radii of curvature and needle electrodes were used for the high potential electrode
Summary
With the generation of lightning voltage, ripple in DC voltagefor occurred kΩ. The peak value of composite voltage is almost 40 kV. MΩ, while no significant ripple was observed for and reduction of the peak voltage was approximately 6.5% for a 526 pF coupling capacitor,for it
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