High‐altitude tunnel‐catenary gap impulse discharge characteristics and breakdown voltage correction

Air gap impulse discharge characteristics of railway tunnel‐catenary at high‐altitude are of great significance to the electrical insulation design.The existing altitude correction methods for non‐uniform air gaps are not applicable to tunnel‐catenary.To investigate the impulse discharge characteristics of the tunnel‐catenary,a typical structural model was built in an artificial climate chamber.Different altitudes were simulated by adjusting the atmospheric pressure.The 50%breakdown voltages of the 300–700 mm tunnel‐catenary gap were tested at 243–4000 m.The test found that the altitude/atmospheric pressure and gap length have an evident effect on the 50%impulse breakdown voltage,and the influence of humidity is relatively small.The polarity effect was analysed by streamer theory.The{d,P,h}parameter method was employed to obtain the fitting formulas for the impulse breakdown voltage.A high‐altitude correction method for the tunnel‐catenary breakdown voltage based on 1 km altitude was proposed.Field natural tests were conducted to verify the accuracy of the proposed method.The results show that the breakdown voltage obtained by the correction method has an average error of 3.66%in the results of the field tests,indicating that the method has engineering application prospects.

Effect of solid particle type,concentration and size on DC breakdown voltage of short needle-plate air gap:An experiment and simulation study

Unclean air discharge refers to the discharge phenomenon of a large number of polluting gases,droplets or solid particles floating in the air,which will cause insulation breakdown and safety accidents for the power transmission equipment that have been left outdoors for a long time.In order to investigate the effects of particle concentration,particle size and dielectric constant on DC breakdown characteristics of unclean air gap,a self-made discharge chamber was designed in this study.The air was filtered and passed into the discharge chamber to remove the influence of impurities contained in the air on the experimental results.Then,solid particles with different concentration,particle size and particle dielectric constant were added to the discharge chamber to carry out the DC positive polarity breakdown characteristic experiment.The experimental results show that compared with dry clean air,the presence of solid particle increases the breakdown voltage of the gap,and the increase proportion of breakdown voltage is related to the particle concentration,particle size and particle dielectric constant.With the same particle type and particle size,the increase proportion of breakdown voltage increases with the higher concentration,which up to 10.49%.For further investigating,the fluid mechanics model was selected to simulate the process of streamer discharge in unclean air.The results show that compared with dry clean air,the presence of particles enhances the gap discharge ionisation process,but also enhances the adsorption of particles,and the latter has stronger effect than the former,thus increases the gap breakdown voltage.At the same time,the enhancement of adsorption effect increases the electric field intensity of the gap and speeds up the development process of streamer discharge.