基于Mach-Zehnder光纤干涉的配电电缆接头局部放电非侵入式声发射检测方法OA

Strengthening partial discharge(PD)detection in distribution cable joints is vital for new power systems.Among current methods,the acoustic emission(AE)technique,employing piezoelectric(PZT)sensors,offers strong immunity to electromagnetic interference and is a reliable option.However,PZT-based AE faces several practical challenges:(1)high costs due to difficulties in distributed applications;(2)severe signal attenuation and distortion over long coaxial cables;and(3)complex multi-point installation in confined cable channels.Recently,fiber-optic interferometric AE sensors have gained interest,with many studies on cable PD detection.Yet,existing research typically embeds fibers inside cables,limiting their use for existing joints.Consequently,designing non-intrusive fiber-optic interferometric sensors that meet sensitivity needs while considering actual cable joint structures remains a challenge. To address these problems,an acoustic emission sensing system based on a Mach-Zehnder optical fiber interferometer was developed.On this basis,this paper introduces the following work. Firstly,a numerical model for the dynamic acoustic pressure sensitivity of a mandrel-type optical fiber sensing unit was constructed based on elastic mechanics theory.This model simulated and analyzed how the mandrel's geometric parameters(diameter,height)and material properties(elastic modulus,Poisson's ratio,density)influence the sensing unit's resonant frequency and peak sensitivity.Simulation results indicate that reducing the mandrel's elastic modulus and increasing its Poisson's ratio significantly improve peak sensitivity.To match the sensing unit's resonant frequency with the 15～35 kHz frequency band of power cable joint partial discharge acoustic signals,smaller geometric dimensions(height=20 mm,diameter=30 mm)were selected.Silicone rubber with low elastic modulus(0.15 GPa),high Poisson's ratio(0.46),and a density of 1 230 kg/m3 was chosen as the mandrel material.A 50 m long G657.A2 single-mode optical fiber was then wound onto this mandrel to construct the fiber optic sensing unit. Secondly,a frequency response test platform was established for the optical fiber sensing unit.Performance calibration results for the developed unit showed a resonant frequency of 40 kHz and a peak sensitivity of 70.1 dB.In comparative tests against a commonly used PZT sensor(Qing Cheng Ltd,G40),the developed optical fiber sensing system achieved a signal-to-noise ratio(SNR)6.0 dB higher at 40 kHz excitation,even after the PZT signal was amplified by 40 dB. Finally,to verify the developed optical fiber sensing system's PD detection capability in real distribution cable joints,two typical defects—a semi-conductive layer step discontinuity and a stress cone misalignment—were created in a 10 kV cable joint for detection experiments.Experimental results confirm the system effectively detects acoustic emission signals from both defects.For the semi-conductive layer step discontinuity,acoustic pulses were detected when the experimental voltage reached 23.0 kV(approx.314 pC apparent discharge).For the stress cone misalignment,detection occurred at 13.2 kV(approx.290 pC apparent discharge). In summary,the developed Mach-Zehnder optical fiber interferometric acoustic emission sensing system can non-intrusively detect discharge signals from typical cable joint defects.With a measurable discharge level around 300 pC,its performance meets the State Grid Corporation of China's enterprise standard for 10 kV cable joint PD,fulfilling daily operation and maintenance needs.