Research On Detection Methods Of Cable Partial Discharge Based On Optical Fiber Sensing

Partial discharge(PD)defect is an important inducement of cable fault.It is very important to find the PD in cable in time to ensure the normal operation of cable.As one of the non electric measurement methods for detecting PD,optical fiber sensing has the advantages of anti-corrosion and anti electromagnetic interference,which can overcome some problems in the field application of electric measurement.Aiming at the PD detection of 10kV XLPE cable,two kinds of optical fiber sensing technology based on Fiber Bragg grating(FBG)and Sagnac interference are studied in this paper.Because the optical fiber sensing mostly realizes the detection function due to the stress of the acoustic signal generated by PD,this paper first studied the diffusion process of the acoustic wave in the cable and the exponential attenuation relationship between the peak-peak value and frequency of the acoustic on the surface of the cable and the propagation distance based on the 10kV XLPE cable body simulation model,and it is clear that the multi-layer structure of the cable body is the main factor leading to the serious attenuation of the acoustic signal,and the attenuation coefficient of the amplitude of the partial discharge acoustic wave of the cable body with the propagation distance is 0.05Np/mm measured by the piezoelectric ceramic sensor.Then,a PD detection system based on FBG was built,and the detection performance of four kinds of FBG sensors was analyzed and compared.It is found that the amplitude of XLPE PD measured by ordinary grating is smaller,and the main frequency is lower than 20kHz,and the phase-shift grating and free end resonance sensor are more sensitive.At the same time,the first and second order exponential attenuation coefficients of PD signal,measured by the free end resonance FBG sensor,are 0.05Np/mm and 0.09Np/mm respectively.Finally,the basic principle of Sagnac interference method for PD detection was introduced.The influence of the material of mandrel,diameter of mandrel,winding method and fiber length of the optical fiber sensor on its detection sensitivity was studied by simulation.The best delay optical fiber length to ensure the system has high sensitivity is 6km,and the PD of XLPE spike-air gap model and suspended potential model was determined by experiments.The results show that the detection effect of this method is better than that of FBG for XLPE partial discharge,and that of suspended potential is better than that of spike-air gap discharge.The phase spectrum of the two kinds of discharge models was calculated by the integrated detection system,and the discharge pulse of spike-air gap model is mainly distributed in the first and third quadrants,while that of the suspended potential model is mainly distributed in the second and fourth quadrants,and the phase distribution of the discharge pulse in the spike-air gap model is more concentrated.