A new method of suppressing the fading effect of phase-sensitive optical domain-of-view reflectometer (Φ-OTDR) by using a phase-modulated frequency comb is presented in this paper. The distribution of fading points is different, so frequency division multiplexing (FDM) radiation can be used to suppress the fading effect. In the experimental system of this paper, firstly, frequency comb continuous light is generated by phase modulation; Then, different Rayleigh backscattering (RBS) intensity distributions are generated by pulse detection light modulating and injecting into the sensing fiber. Finally, the intensity distribution of RBS is extracted by amplitude estimation method. The phase is processed to eliminate the missing truth. The fading suppression is realized by our system, and the suppression effect is evaluated. By using a constant amplitude optical frequency comb with seven frequency components, the fading probability of the system is drastically reduced from 5.49%-9.83% to 0.08%. The method proposed in this paper has larger modulation bandwidth and more flexible frequency combination scheme, which can better suppress the fading effect. This method does not sacrifice the response bandwidth of the system, and can accurately control the phase delay, so it is very helpful to fully suppress the fading effect.
In order to measure fiber strain using distributed fiber strain sensing technology, the strain of three composite submarine cables is reflected. The on-line stress monitoring and intelligent early warning technology of long-distance and highprecision distributed fiber optic sensing submarine cable are studied, and the stress decoupling method of Brillouin distributed fiber based on fiber Brillouin scattering model is realized. Finite element simulation method is used to calculate conductor core strain through optical fiber strain. Combined with finite element simulation analysis, stress distribution characteristics of different stress damage modes of submarine cable such as anchor breakage, anchor hook and hanging are obtained, the alarm threshold of submarine cable stress anomaly is proposed to complete intelligent early warning of submarine cable stress anomaly. It also provides a theoretical basis for submarine cable routing and topographic information anomaly location and typical submarine cable fault diagnosis.
Submarine cables are used in 500kV power transmission station. Insulating fluid was filled into the cables to protect them. There is a set of insulating fluid pumping station in Nanling and Linshi. The corresponding control systems were equipped to achieve the automatic control of insulating fluid pumping station in Nanling and Linshi. The control systems could meet different operating conditions. The rate and the pressure of the flow could be changed according to the set values by the control systems. The send-out and take-back of the Insulating fluid in Nanling and Linshi can be alternated by the control systems. The cables could be protected from seawater if the cables were damaged. The operation information could be sent to Fuzhou control center. The control system is built with the ControlLogix controller of AB. Different modules were used to collect signals according to different equipment types on site. The signals should be calculated, analyzed and optimized. The operations of the submarine cables could be acquainted according to the signals. The rate and direction of the Insulating fluid flow could be changed by the control system by starting or stopping the pump. Insulating fluid pressure at the outlet of submarine cable was maintained in the relative range and Insulating fluid flow remains at maximum in normal operation mode. Insulating fluid pressure at the outlet of submarine cable was maintained Above the minimum and Insulating fluid flow Decrease from maximum to the minimum In Emergency mode. The control system could meet the daily operation requirements of submarine cable stably after monitoring and recording long- term operation of the system. It could alert when the oil pump system was abnormal.it can protect the submarine cable from the seawater In emergency mode and the Insulating fluid would be the minimum to protect the environment.
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