| Flexible high-voltage DC transmission technology plays an important role in long-distance transmission systems.The main equipment that undertakes electrical energy conversion is a converter valve.The high-voltage power electronic switching device of the converter valve,such as IGBT,is subjected to pulsed electrical stress during the switching process,and there is a risk of electrical aging failure of the insulating material.By studying the partial discharge characteristics and insulation aging life of the insulating material,the law of the insulation failure of the material under pulsed electrical stress is obtained,which is beneficial to improve the reliability of the entire power system.Firstly,a spherical plate electrode device system with a slightly uneven field was developed,and a partial discharge experimental platform for solid insulating materials under a high-frequency nanosecond pulse voltage was established.Based on the analysis of equivalent RLC series circuits,the influence of displacement current was eliminated,and a statistical graph program for partial discharge of insulating materials under high-voltage and high-frequency pulse was designed.The effects of voltage amplitude,frequency,rising edge,and pulse width on the partial discharge characteristics of the polyimide film were studied.Secondly,based on the electrical,acoustic,and optical characteristics before and after the breakdown of the insulating material,an insulation life curve that reflects the influence of a single parameter on the life of the insulating material was obtained and the effects of voltage amplitude,frequency,rising edge,and duty cycle on the insulation life of polyimide films were studied.Combined with X-ray photoelectron spectroscopy and optical emission spectroscopy,elemental changes before and after breakdown were obtained,and electrochemical aging was considered to be the main cause of polyimide film breakdown.Finally,the partial discharge characteristics,insulation life,and breakdown voltage under nanosecond pulses and the same-frequency AC impact were compared and studied.It is found that although the amplitude of a single discharge current generated by partial discharge under pulse voltage is higher than the amplitude of discharge current under AC voltage at the same frequency,the number of partial discharges under the same frequency AC voltage in one cycle time is more,and is more dispersed than that under the nanosecond pulse voltage.When amplitude of the nanosecond pulse is consistent with that of the same-frequency AC,the former has a longer insulation life than the latter. |
PDF Full Text Request