Study On The Transfer Function Of Partial Discharge Radio Frequency Signal In The Intermediate Joint Of Cross-linked Polyethylene Cabl

A cable joint is an important part of a power cable.Due to possible flaws in the manufacturing process,cable joints may contain defects such as cracks and protrusions in cable inner semi-conductive（semicon）layers,and semicon remains and scratches on cable insulation.Such defects are prone to partial discharge（PD）during operation of the cables.Continuous PD can accelerate the aging of the joint insulation,leading to a shortened service life of the cable joints,and potentially affecting the safety and reliability of the power system.PD detection is effective for testing the insulation integrity of cable joints,and the detection method frequently used is electrical methods.Electrical methods can be divided into conventional methods and non-conventional methods,and the non-conventional method of radio frequency（RF）detection can achieve non-invasive measurement,so it has potential advantages for improving the signal-to-noise ratio and achieving PD location.In this paper,the following work is carried out for RF detection of PD in cable joint.First,the paper reviews the current status of research on PD in cable joints and several research methods of PD propagation characteristics and determines the research focus and significance of this paper.That is,the propagation characteristics of the partial discharge signal in the cold shrink joint are investigated by using the FDTD.Secondly,a FDTD model of 35k V single-core XLPE cable joint is established by XFdtd.The transfer function（TF）of the discharge signal was calculated by defining excitation sources with different directions and positions in the model to represent the PD of different defects and locations in the joint.The results show that the magnitude and shape of the TF are closely related to the position and direction of the excitation source in the model.Moreover,the TF magnitude for the excitation source defined in the radial direction of the cable joint model is found to be generally more than one order larger than that of the same source defined in the axial direction.Finally,the effectiveness of the FDTD model in representing high frequency properties of the cable joint has been checked against both time domain reflectometry（TDR）and S₂₁ measurements on a cable joint made in laboratory.The TF results from this work are expected to be helpful for applications of radiometric PD detection to cable joints,e.g.,enabling improvement of the detection sensitivity through optimizing frequency responses of RF sensors.