| Optical fiber composite overhead ground wire is to place optical fiber in the ground wire of overhead high-voltage transmission line to form the optical fiber communication network on the transmission line.It is an important development direction of power special optical cable.With the construction of optical fiber communication network in power system,the investment of OPGW optical cable is greatly increased.How to protect the safe operation of OPGW cable has become a crucial link.In practical applications,OPGW cable is usually subject to lightning and icing disasters.Lightning will cause high voltage transmission line trip accidents,most of the trip accidents are caused by lightning.At the same time,lightning can also cause transmission line flashover,damage the stability of the power system,and even cause a large area power outage;when the temperature reaches 0℃in the south of China in winter,the outdoor OPGW optical cable will appear icing phenomenon,which will increase the tension between the optical cables.When the tension of the optical cable is too large,it will cause ground wire breakage,tower collapse accident,etc.In order to realize the real-time monitoring of OPGW cable,this thesis proposes a method to monitor the temperature and vibration of OPGW cable based on the grating array sensing technology.The operation status of OPGW cable is monitored through the temperature and vibration information,and the lightning accident and icing status are qualitatively analyzed through the monitored information.In this thesis,grating array temperature and vibration sensors are added to the structure of OPGW optical cable,and the temperature and vibration information along the optical cable is monitored in real time by the number advantage of grating array.The real-time temperature of the optical cable is used to analyze whether it is struck by lightning.At the same time,using the vibration information,a method based on the string vibration model to monitor the tension value of the cable in the wind-induced vibration is proposed.The vibration signal is processed by MATLAB software and the wavelength demodulation algorithm is designed to restore the vibration frequency and standing wave wavelength of the OPGW cable in the wind-induced vibration.The tension value of the OPGW cable is calculated by combining the frequency and wavelength values with the string vibration model to analyze the icing state State.The main work of this thesis is as follows:(1)This thesis first introduces the lightning and icing disasters encountered by traditional transmission lines during outdoor operation,as well as the disaster situation all over the world in recent years.The new optical fiber composite overhead ground wire(OPGW)with optical communication unit added to traditional transmission lines is more vulnerable to disaster than traditional transmission lines.However,there are many disadvantages in the traditional transmission line monitoring methods,so a new method using optical fiber sensing technology to monitor the operation of OPGW appears.In this thesis,the research status of optical fiber sensing technology in OPGW monitoring is introduced,focusing on the research status of using weak grating array sensing technology to monitor OPGW.(2)This thesis introduces the principle of optical fiber sensing technology based on weak grating array to monitor OPGW cable.Firstly,the basic principle of fiber grating sensing and the time division multiplexing principle of weak fiber grating are introduced.From two aspects of temperature monitoring and vibration monitoring,the principle of the corresponding sensing system and the corresponding signal demodulation technology are introduced.Then the structure and application of weak fiber Bragg grating sensor in OPGW are introduced.(3)The temperature monitoring of OPGW cable based on weak grating array sensing is introduced.Firstly,the structure of a weak grating array temperature sensor in OPGW is simulated,and the lightning strike simulation experiment is carried out using this structure.Then,high and low temperature chamber experiment and lightning strike experiment are carried out with actual OPGW cable,and the experimental data are processed and analyzed.To verify the feasibility of monitoring OPGW lightning strike and temperature by grating array temperature sensing technology.(4)The vibration monitoring of OPGW cable based on weak grating array sensor is introduced.Through the vibration monitoring of OPGW cable,the tension value of the cable is obtained,and the ice condition of the cable is described by the tension value.Firstly,the theory of string vibration standing wave and the conditions of its application in OPGW cable are introduced.The vibration information is collected by the OPGW vibration monitoring system,and the corresponding demodulation algorithm of the frequency of string vibration and the half-wavelength of standing wave is designed.Then,through the data obtained from the wind induced vibration experiment,the OPGW cable is validated by using the string vibration standing wave model.Then,according to the demodulation algorithm,the frequency and half wavelength of standing wave of OPGW cable vibration are obtained,and the feasibility of calculating the tension value by grating array vibration sensing technology is verified,and the error of the tension value calculated by this method is analyzed. |
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