Effect Of X-ray On Partial Discharge Of XLPE Cable Accessories

Crosslinked polyethylene(XLPE)cable accessories are prone to cable failures every year due to metal particles at the XLPR/SIR interface and surface discharge defects.In the cable handover test,when the defect size is small,there is a situation of missing defects.At present,X-ray excited partial discharge has been widely used in the detection of epoxy resin bubble defects.X-ray irradiation can change the characteristic quantity of defect discharge and improve the detection sensitivity.In this paper,pulse current method is used to detect partial discharge,and the influence of X-ray on defects is studied by analyzing the initial voltage,discharge repetition rate,maximum discharge amount,average discharge amount and Δ t spectrum of partial discharge with and without X-ray irradiation.The models of metal particle defects and semi-conductive spike discharge defects at the interface of XLPE/SIR are made,a set of partial discharge detection system under X-ray irradiation is built,the dose rate of X-ray at the defect is calibrated,the partial discharge is detected by pulse current method,and the measurement platform of X-ray attenuation characteristics in cable materials under different tube voltages is built.The effect of X-ray on the discharge of metal particle defects at the interface of XLPE/SIR is studied,including changing the thickness and shape of metal particles,changing the tube voltage of the X-ray machine and the direction of applied electric field.Under X-ray irradiation,the partial discharge inception voltage of metal particles with thickness of 0.1mm,0.5mm and 1mm are reduced by 11.4%,12%and 20.3%,respectively.X-ray reduces the partial discharge inception voltage of triangular,square and circular metal particles by 12.0%,14.1%and 13.5%,respectively.The amplitude of the decrease of the partial discharge inception voltage of 0.5mm thick metal particles by X-rays with different tube voltage is the same,which is 12%.Compared with the vertical electric field,X-ray has a greater reduction in the partial discharge inception voltage of metal particles under the orthogonal electric field,with a reduction of 29.34%.X-ray can reduce the defect discharge delay and increase the discharge repetition rate,and the effect mechanism of X-ray on interface metal particles partial discharge is analyzed.The effect of X-ray on the semi-conductive spike discharge of XLPE/SIR is studied,including changing the external applied voltage and the tube voltage of the X-ray machine.X-ray has no effect on the starting voltage of partial discharge without bubbles in front of the spike along the surface.X-ray reduces the partial discharge initiation voltage of semi-conductive tip-prickling bubble defects by 14.7%.The reduction amplitude of partial discharge initiation voltage of π×12×2mm3 bubble defects by X-rays with different tube voltages is the same,which is 14.7%.The influence mechanism of X-rays on bubble defects is analyzed.The attenuation characteristics of X-ray in the materials used in the cable under different tube voltages are studied.With the increase of material thickness,the transmission dose rate and equivalent attenuation coefficient of X-ray become smaller and smaller.Compared with metal materials,the non-metal transmission dose rate is higher and the equivalent attenuation coefficient is smaller.When the interface metal particle defects are fabricated on the 10 kV XLPE cable terminal,the X-ray reduces the PDIV by 7.3%,which verifies the effectiveness of the X-ray application in the actual XLPE cable terminal defects.