| With the advancement of our country’s urbanization,the requirements for the safety and reliability of the distribution network are gradually increasing.The power cable is an important component of the distribution network.It can timely and accurately detect and solve the fault of the cable,which is beneficial to ensure the stable operation of the distribution network.Optical fiber sensing detection technology is different from traditional detection methods.It has long detection distance,high sensitivity,strong antiinterference ability.And it can also measure parameters on the entire optical fiber link,with good real-time performance.This paper proposes the cable discharge fault detection scheme based on optical fiber vibration sensing technology.It bring forward the way of detecting the cable faults.First,focus on the discharge equivalent circuit.By using the electrical-electrical analogy,the vibration generation mechanism under the discharge fault can be deduced,and the relationship between the external vibration signal and the phase change can be obtained.We analyze the optical fiber vibration sensing of φ-OTDR systems with different structures.Theoretically,it is feasible for the fiber-optic vibration sensing technology to realize cable discharge fault detection.The vibration signal caused by cable discharge has the characteristics of low amplitude and high frequency.In this paper,we propose an optimized FDM-φ-OTDR system based on the double-pulse direct detection structure.On the one hand,this system can restore the comprehensive phase information of the external vibration and save the experimental cost.On the other hand,the system is processed by frequency division multiplexing technology,and the frequency response bandwidth is improved.So,it is more suitable for high frequency vibration detection.In order to improve the positioning accuracy of the system,this paper combines the wavelet packet denoising with the amplitude differential positioning method.The discretization modeling experiment has verified that the system can detect and locate the high-frequency vibration signal of20 k Hz.To solve the problem of amplitude error and total harmonic distortion caused by the influence of modulation depth on the demodulation effect,this paper proposes an improved PGC-DSD-Arctan demodulation algorithm.Through theoretical derivation and simulation,it is proved that the improved algorithm is not affected by the parameters of the signal to be measured.The algorithm demodulation effect is more stable.And it basically eliminates the dependence of demodulation results on modulation depth.Finally,we build a high-frequency vibration detection platform and a cable discharge fault detection platform based on optical fiber vibration sensing.The experimental clearly detect the vibration signal caused by the fault.After repeated experiments,it proves the feasibility of the system. |
