Study On Process And Model Of DC Ice-melting On Optical Fiber Composite Overhead Ground Wire(OPGW)

Atmospheric icing on overhead transmission line poses a serious threat to the safe and stable operation of power grid.Optical fiber composite overhead ground wire(OPGW)bears lightning protection and communication function,which has been widely used in the power grid.However,with more serious icing degree and lower design strength than conductors in the same condition,OPGW has become a weak link in the ice disaster prevention of transmission line.The accidents caused by atmospheric icing on OPGW,such as short circuit trip,line disconnection,hardware falling off,tower broken or collapsing,which lead to the interruption of power communication and affect the normal operation of power system.Among the methods dealing with the icing problem of transmission line,DC ice-melting is a mature and feasible technology,which can effectively reduce the icing degree of the lines and the damage of the power system.Although the DC ice melting technology of transmission line has been relatively mature,the study on ice-melting of OPGW is still in the initial stage.When the DC ice-melting technology is applied to OPGW,the unreasonable selection of ice-melting current in the DC ice-melting process would result in burnt of OPGW and the increasing of fiber attenuation.Therefore,establishing a DC ice-melting model for OPGW,to confirm the ice-melting current,ice-melting time and temperature rise of OPGW,which can provide a reference and guidance for the implementation of DC ice-melting scheme for OPGW,and has very important engineering application value for prevention of large area ice disaster accident of power grid.Firstly,according to the physical ice-melting process of OPGW,the dynamic numerical calculation model of DC ice-melting for OPGW is established based on the heat transfer principle.The model is applied to simulate the dynamic change process of temperature field distribution of ice and OPGW,and analyze the factors affecting DC ice-melting for OPGW.Then,the DC ice-melting model for OPGW are verified by a large number of DC ice-melting experiments conducted in artificial climate chamber and natural icing test station.Finally,the ice-melting current selection method for OPGW is proposed based on the simulation and experimental results,and the formulas of the ice-melting current and maximum permissible ice-melting current are obtained.The main results are follows:For two different kinds of OPGW lines,the dynamic numerical calculation model of DC ice-melting is established.The current distribution of OPGW and the variations of heat exchange between ice layer and surrounding environment have been taking into account in this model,and the growth process of air gap has been analyzed.Based on the simulation of DC ice-melting model,the ice-melting time and the temperature variations of optical fiber in the ice-melting process have been obtained.Results show that the heat exchange lose at the outer surface of ice layer increased with rising of temperature of OPGW and ice layer in the ice-melting process,resulting in slower ice layer's melting rate and temperature rising rate of optical fiber.At the ice-shedding time,temperature of optical fiber in OPGW reaches the highest.According to the temperature variations of optical fiber in the ice-melting process,the maximum temperature of optical fiber is analyzed and calculated.The maximum temperature of optical fiber in the whole ice-melting process is determined by the temperature in pre-ice-shedding stage and post-ice-shedding stage.The highest temperature of optical fiber in the pre-ice-shedding stage is the temperature at the ice-shedding time,which is mainly affected by the ice melting current and ice thickness,regardless of ambient temperature and wind speed.However,the temperature of optical fiber in the post-ice-shedding stage is influenced greatly by the ambient temperature and wind speed.When wind speed is big or ambient temperature is low,the temperature of optical fiber is higher after ice shedding from OPGW.A large number of DC ice-melting tests for OPGW have been carried out relying on the experimental platform in artificial climate chamber and natural icing test station.The results indicates that the variations of optical fiber temperature according to the simulation results of DC ice-melting model are similar with the experiment results.And the numerical results of ice-melting time and optical fiber temperature under the conditions with different ambient temperature,wind speed,ice melting current and ice thickness are in accordance with the test results.Based on the simulation and experimental results,the temperature of OPGW and residual ice layer at ice-shedding time are calculated out,and the formulas of the maximum temperature of the optical fiber in the whole ice-melting process is obtained.Then,according to the heat balance relationship in the DC ice-melting process,the formulas of the ice-melting current and maximum permissible ice-melting current for OPGW are put forward.Results show that the ice-melting current of OPGW is mainly determined by the wind velocity,ambient temperature,ice thickness and ice-melting time.Under the condition with low ambient temperature or high wind speed,the maximum permissible ice-melting current of OPGW depends on the icing thickness.