Influence Of Cumulative Effect Of Mechanical Impact On Breakdown Characteristics Of Thermally Aging Insulating Paper

The power transformer is one of the core equipment of the power system,and the insulation state of its internal oil-paper structure directly affects the safe operation of the transformer.Transformers often suffer load short-circuits during operation,and the cumulative damage caused by multiple short-circuit currents and electrodynamic impacts seriously affect the dielectric properties of the oil-paper insulation structure.At present,domestic and foreign studies have been carried out on the cumulative effect of oil-paper insulation,but the research is mainly focused on the impact of electrical stress impact such as lightning impulse voltage and operating overvoltage on the insulation performance,and the electromotive force caused by the sudden current change also causes serious insulation performance.Therefore,it is necessary to carry out research on the cumulative effect of mechanical impact on thermally aging insulating paper.This paper first designs and builds a mechanical impact damage experiment device that simulates short-circuit electric power,and produces insulating paper samples with different thermal aging degrees,and gives the specific preparation process and testing standards of the samples,and makes a mechanical impact damage plan with reference to a large number of related documents.And the insulation paper sample after thermal aging has been impacted treatment.The initial partial discharge voltage and breakdown voltage of the insulating paper after the treatment were measured,and the microstructure of the sample was observed and analyzed with a super-high magnification lens zoom microscope,and the effect of cumulative mechanical impact on insulating paper is studied by comparing the samples that have not been subjected to mechanical impact from both breakdown characteristics and microstructure.Statistics on the crack development law of samples with different aging times under various impact strengths were carried out,and a mathematical model of the influence of mechanical impact damage on the breakdown voltage of oil-paper insulation was established on this basis.Research shows that with the increase of mechanical impact strength,number of impacts and thermal aging time,the breakdown voltage of insulating paper and the initial voltage of partial discharge show a general downward trend.Under pure DC,50% AC content and pure AC voltage,the initial partial discharge voltage of the insulating paper increases first and then decreases under low impact strength,but only decreases with the increase of the number of impacts under medium and high impact strength.Consistent with the change rule of breakdown voltage,and the increase of impact strength and aging time increases the degree of data decline,and the breakdown voltage decreases more obviously with the DC component increasing.Mechanical impact makes the surface of the insulating paper rough and cracks inside the insulating paper.The le ngth and depth of the crack gradually increase with the increase of impact strength and frequency,until the structure of the insulating paper is destroyed,and thermal aging promotes the destructive effect of mechanical impact.The model calculation results of the influence of mechanical impact damage on the breakdown voltage of oil-paper insulation are basically consistent with the experimental trend.