Research On Radio Frequency Detection Of Partial Discharge In Cross-linked Polyethylene Intermediate Joint

Insulation defects are more likely to occur in cable intermediate joints made in the field,and these defects may cause partial discharges after the cable is put into operation,leading to accelerated aging of the joint insulation.RF detection of partial discharge can achieve noninvasive measurement,but it is still relatively little used in the detection of partial discharge in cable intermediate joints.In this paper,we use the need to reserve a break in the outer conductor shield of the joint when the cable intermediate joint is grounded by crossinterconnection to set a near-field sensor at the break to couple the discharge signal inside the joint.A 35 k V prefabricated cold-shrink intermediate joint was used to build a partial discharge RF detection experimental platform to produce internal air gap defects,while an FDTD simulation model was established based on the structural parameters of the cable joint to conduct a joint partial discharge RF detection study.The results of the time-frequency analysis of the RF signal of partial discharge in cable joints show that the waveforms of discharge pulses detected by electric field and magnetic field sensors at the same detection position and voltage are generally similar,and the frequency spectrum is mainly distributed in the 10-200 MHz band.The magnetic field has a greater spectral density in the 10-100 MHz band,and the electric field has a greater spectral density in the 100-200 MHz band.As the pulse amplitude and total number of discharge pulses at different voltages increase,the ratio of the energy in10-100 MHz to the total energy of the spectrum also increases and gradually stabilizes.Through experiments and simulations to analyze the factors affecting the RF detection of partial discharge in cable joints,this scientific research has concluded that,in the radial direction of the joint,as the RF sensor distance increases,the amplitude of the discharge pulse shows a trend of exponential decay with distance,while its spectral energy in the 10-100 MHz band accounted for a decrease,while the 100-200 MHz band accounted for an increase.As the size of the copper shield break increases,the amplitude of the voltage signal detected by the sensor shows a power exponential increase,while the spectrum distribution will be more dispersed.The results of this paper initially verify the feasibility of detecting partial discharges in cross-interconnected grounded cable intermediate joints by RF methods,determine reasonable detection frequency bands,and are expected to enable a new non-intrusive partial discharge detection method.