Research On DC Corona Discharge Of Transmission Line Defects In Corona Cage Based On Experiment And Simulation

The surface defects of DC overhead transmission lines can cause local field intensity distortion.When the electric field near the defect exceeds the critical corona field strength,corona discharge can occur.Corona discharge of defective line usually occurs near the tip burr with high field strength.Based on small corona cage,the corona discharge characteristics of defective line under the influence of multiple factors were studied by experiment and hybrid numerical simulation.A set of experimental research platform for DC corona characteristics of defective line was designed and built.The relative humidity in the test cavity can be adjusted in the range of 15%-95%,and the air pressure can be adjusted in the range of 50k Pa-101.3k Pa.The test and finite element simulation results showed that the ratio of breakdown voltage to corona inception voltage was 1.24,which meets the design requirements.The distortion rate of electric field on the line surface caused by the designed observation window was less than 5%,and the parameters of cavity and corona cage are designed reasonably.The positive DC corona discharge characteristics of the line under different environmental factors and defect geometric structures were obtained.The corona discharge parameters,such as corona inception voltage,discharge current,ultraviolet and visible light images of 5/7.5/10 mm radius defective lines were studied.The corona inception voltage decreases with the increase of burr height,the decrease of burr tip curvature radius,line radius and air pressure,and decreases first and then increases with the increase of relative humidity.A fter the inception of the corona discharge,the long exposure visible light image shows a fan-shaped luminous region,and the discharge current shows the pulse characteristics of stable amplitude and increasing frequency with the increase of voltage.The c orona inception criterion based on the spot area was pro posed,which basically consisted with the voltage obtained by the conventional corona inception criterion.Based on the hybrid numerical model of fluid mechanics and chemical reaction,the spatiotemporal evolution characteristics of each micro characterist ic quantity in the corona discharge process of defective line were obtained.In this paper,12 kinds of particles and 35 kinds of plasma chemical reactions in air environment were analyzed,and the calculation parameters of energy loss,reaction rat e and collision cross section data of each reaction were determined.During corona discharge,the maximum electric field strength and electron temperature appeared at the head of streamer,and the electron density of the head was about 1×10²⁰ m^-3;the rise time of discharge current was about several or more nanoseconds,and the decay time was about 500 ns.The simulation results of corona current and corona inception voltage were consistent with the experimental results.