| With the social development and the process of industrialization, it becomes more popular to design City Transmission Line using HV cables. Compared to conventional overhead lines, using HV cables need for more spending, and thus how to improve the transmission capacity of cable lines, and how to improve equipments' utilization will become a long-term concern in the electric power research field.In this paper we will discuss the steady-state and cyclic current rating of HV cables. First we will introduce the underground cable thermal model in IEC 60287, IEC 60853 and give its algorithm and formulas. Second we will collect information about the typical designs and laying conditions for HV cables in Shanghai, and gather some load curve data related to those cables. Then we will set up the model and do some simulation and calculation. We will give the range of cyclical fact and try to analyze the measures to improve utilization of cable in the conclusion.220kV Chongming Interconnection Project is the world's largest tunnel-bridge cable laying project under construction. In the project HV cable will be laid in different environment and different conditions, and this will lead to some difficulties in ampacity calculation. In this paper we will investigate some cable section in this project, and analyze the thermal field in duct environment and in Yangtze River Bridge box girder environment. We will set up the thermal model and do some simulation and calculation. In the conclusion we will review the cyclical factor of the cable and give some tips when using cyclical current rating calculation. Using the cyclical current rating concept in operation can increase the efficiency of HV cable equipment and reduce wastage of resources. Also this work can review the transient operation of cable running from the theoretical point of view, and provide guidance to ensure the safety of cables running.
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