Research On Leakage Field Vector Calculation And Distribution Law Of Steel Core Broken Strands Of High Voltage Transmission Lines

Most of the wires used in high-voltage transmission are aluminum conductor steel reinforced,and the steel core inside the deep aluminum wire is the main tensile carrier.The detection of magnetic leakage from broken steel cores has been one of the challenges that has received much attention and still has low accuracy.The study of the distribution law for the detection of broken strands of aluminum conductor steel reinforced is of great significance for the prevention of breakage accidents and the reliable operation of transmission line.In view of the existing research on the leakage field of broken steel cores,which only considers the geometric parameters such as the length,width and depth of the broken strands,this paper takes into account the actual structure of the conductor and successively uses Ansoft Maxwell software to analysis the influence of the distribution law of the leakage field of broken steel cores based on the simplified smooth column conductor model,the steelcore aluminum strand model and the transient strand wave conductor model.The main work and conclusions of the paper are as follows:1)Firstly,the distribution rules of the leakage vectors Bx,By and Bz were analyzed for twelve strand break angles using a simplified wire model.The results show that the vectors Bx and By have a multi-peaked pattern,and the distribution of positive and negative peaks is reversed at 90° of the broken strand as the dividing point.The vector Bz has multiple peaks at 90° due to the width of the broken strand,while the other vectors have a single peak pattern.The peak comparison shows that the positive and negative peaks of Bx and By are less than 5%of the peak of B-,and the vector Bz is the main component and the most sensitive to the broken strand of the steel core,the Hall element should be arranged perpendicular to the surface of the wire to pick up the vector Bz as the most effective signal detection direction.2)Secondly,based on the stranded wire model,the distribution of magnetic leakage vectors for different number of broken strands was investigated with the premise of whether the inner layer of steel wire is broken or not.The results clarify that the leakage vectors Bx and Bz can show the distribution pattern of the leakage field of the breakage more obviously,while the vector By is dominated by the strand wave signal.A comparison of the peak values of vectors Bx and Bz reveals that the effect of strand breakage on the leakage magnetic field is greater in the inner steel wire than in the other strands,and that the calculated amplitude of the leakage flux generated by the other strand breaks is reduced when no strand breakage occurs in the inner steel wire.3)Finally,the differences in the strand wave signal shapes,the different damaged locations and the static transient leakage vectors are analyzed in conjunction with a transient strand wave conductor model.The results show that the wave signal is a periodic signal which similar to a sine wave.The peak change in vector Bx is only about 18.1%of vector By when the single strand position is damaged,while the peak change in vector By is only about 54.2%of vector Bx when the interstrands position is damaged.The transient is somewhat reduced in magnitude for each leakage vector compared to the static calculation,and the wire motion is more likely to have a greater effect on the axial signal.The transient calculation increases the wave width of the vector Bx wave form and the peak spacing of the By wave form,with the static wave width of Bx being only about 30%of the transient and the static peak spacing of By no greater than 30%of the transient.