| As a key medium to realize the power supply between inland and island,offshore platform and offshore wind farm,submarine cable is a strong guarantee for coastal economic development and resource development.With the development of marine power strategy,the scale of interconnection between coastal islands and inland power supplied network is expanding.The safe and stable operation of submarine cable network is of great crucial to social stability and economic development.In view of the special operation environment,high experimental cost and difficult state information acquisition of photoelectric composite submarine cable system.In this paper,we analyze the coupling effects between electric field,thermal field,force field and optical field in the photoelectric composite submarine cable system based on COMSOL Multiphysics.We construed the numerical mode of photoelectric composite submarine cable.The influence of laying depth,ambient temperature(seasonal variation),heat transfer coefficient between sea water and sea soil on the working temperature of submarine cable core and the response time of submarine cable under overload condition are explored.The main research contributions of this paper are as follows.(1)The electromagnetic loss and other key electrical parameters of the submarine cable under rated current carrying capacity are studied and analyzed by using the electrical analysis model of three cores photoelectric composite submarine cable.It is found that the temperature effect of the resistance is about 20% higher than that of the cable core without considering the temperature effect,but the loss of armor and shielding layer is decreased.For the shielding layer and armor,the internal current is induced by the electromotive force generated by the copper conductor of the cable core,which is voltage driven,which is just opposite to the cable core driven by current.(2)The coupling model of electric thermal multi physical field of three cores photoelectric composite submarine cable is established,and the relationship between the cable core temperature and the heat transfer coefficient between sea water and sea soil is studied at different laying depth and different ambient temperature.It is found that the influence range of submarine cable on sea soil temperature is about 1.5m,which is relatively limited,while the influence of heat transfer coefficient between sea water and sea soil on submarine cable can be ignored;however,the influence of environmental temperature on the working temperature of submarine cable is great.With the increase of environmental temperature,the working temperature of submarine cable core will also increase obviously,so the environmental temperature change must be considered in the monitoring signal.The influence on submarine cable.(3)Based on the coupled model of electric thermal multi physical field of three core photoelectric composite submarine cable,the temperature change of each layer of submarine cable under the condition of overload operation with daily period and degradation of XLPE insulation layer with different carrying capacity is analyzed.It is found that the emergency time of submarine cable is 19 h,10h and 7h under 180%,200%and 230% of excess rated flow respectively;with the increase of degradation degree of XLPE insulation layer,the rise of cable core temperature almost increases in direct proportion,and with the increase of ampacity,the temperature rise of cable core is more obvious.(4)Based on the 3D numerical model,the electrical faults such as electric leakage and grounding short circuit of photoelectric composite submarine cable are analyzed and studied.It is found that the temperature of the optical unit along the length direction of the submarine cable is the highest at the leakage position,and the temperature gradually decreases along the two sides of the leakage location.The width of the influence area of the leakage location on the temperature of the optical unit is about 5m.When the leakage power is 2W,6W,10 W,14W and 18 W,the maximum temperature rise of the optical unit at the leakage position is 0.72℃,2.16 ℃,3.61℃,5.05℃ and 6.49℃.The increase of degree is linear.After the submarine cable grounding fault occurs,the maximum temperature of the optical unit increases with time as the heat is continuously transferred from the fault location to the optical unit.The temperature of the optical unit close to the power supply side is higher than that of the optical unit far away from the power supply side owing to short-circuit current.(5)In this paper,the electrical fault characteristics were concluded.Based on the coupling reactions among different physical fields,a distributed online fault monitoring system based on BOTDR optical fiber is proposed. |
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