Research On The Coding Technology Of Rayleigh BOTDA For Monitoring Transmission Line Icing

In power systems,transmission lines are affected by natural disasters,thus the operation of power systems suffer icing accidents threatened seriously.Therefore,monitoring the icing situation of transmission lines is of crucial importance for power system protection,and research on the technology of monitoring the icing situation of transmission lines has become a hot topic.In this paper,the coding technology of coded Rayleigh BOTDA,used in monitoring the icing situation of transmission lines,has been studied.The main content of this paper is listed as follows:(1)All methods of monitoring the icing situation of transmission lines are summarized.Five kinds of BOTDA based on distributed optical fiber sensors are compared,after that,the Rayleigh BOTDA is the most suitable one for monitoring the icing situation of transmission lines.(2)The mechanisms of spontaneous Brillouin scattering and stimulated Brillouin scattering in optical fiber are introduced.The rules of Brillouin frequency shift and Brillouin scattering intensity changing with temperature are studied.Transient-state and steady-state coupled wave equations are analyzed and the theoretical model of Rayleigh BOTDA is established based on steady-state coupled wave equation as well as the principle of Rayleigh BOTDA.Then,the paper research on the relationship between the Rayleigh scattering light power,Brillouin scattering light power,the pump light power with the length of the fiber.(3)The relationship between spatial resolution and pulse width in Rayleigh BOTDA is studied.Techniques of superposition averaging technique,Simplex coding technology,Golay complementary sequence coding technology and complementary correlated prometheus orthonormal sequence coding technology,can be used to improve signal-to-noise ratio(SNR)under the premise of maintaining the spatial resolution.According to the principle,the gains of L times superposition averaging,L bits Simplex coding,Golay complementary sequence coding,CCPON sequence are(?),(L+1)/2(?),(?)/2 and(?)/2,respectively.Furthermore,the time domain output signal improvement of Rayleigh BOTDA based on the four technologies is simulated and analyzed with the use of MATLAB.(4)The principle of pulse coding Rayleigh BOTDA to monitor transmission line icing is analyzed and the feasibility is verified by simulation.The combination between superposition averaging technique with Simplex coding technique,Golay complementary sequence coding technique and CCPON sequence coding technique is studied and applied in Rayleigh BOTDA to monitor the icing situation of transmission lines.From the perspectives of temperature and Brillouin spectrum,simulates the improvement of signal to noise ratio by Rayleigh BOTDA based on three kinds of coding methods including 7 bits Simplex coding,8 bits Golay complementary sequences,8 bits CCPON sequences combine with 9 times superposition averages.By simulation,one can find that,the measurement accuracy of three combined coding techniques increased by 0.02 times,0.33 times and 1.64 times,respectively.Besides,the dynamic range of three combined coding techniques increased by 0.55dB,1.57 dB and 3.62 dB.