Modeling Of Deepwater Vertical Multi-core Cable

With the development of marine economy,the research on underwater cables has gradually attracted people’s attention.Vertical multi-core cable is used in marine operations.It is critical equipment for connecting mother ship facilities and underwater systems.The analysis of the power transmission characteristics of the cable is the premise of the functional design of the entire deep-sea operating system.Obtaining the transmission performance of the cable through testing is time-consuming and labor-intensive.Therefore,analyzing the cable through model can effectively simplify the system design and improve the design efficiency.At present,many studies at home and abroad use analytical and numerical methods to analyze underwater cables.Most of these analyses focus on their mechanical properties and manufacturing design.There are few analyses on their electrical transmission performance,and these analyses have remained on simple horizontal cables.However,the complex coupling relationship inside the multi-core cable and the dynamic changes in circuit parameters caused by vertical placement cannot be ignored.In order to study the pressure drop and energy loss along the deepwater vertical multi-core cable during power transmission,a dynamic model was established for the particularity of its placement,internal structure,and application environment.This dynamic model is different from the existing ordinary cable models,and the differences are mainly reflected in three aspects: first,as a vertical cable,its parameter calculation dynamically changes with the depth of the ocean;second,the parameter calculation is classified and discussed according to the positional relationship of the internal conductor;third,the influence of the sea floor and seawater medium is taken into account in the parameter calculation.In this paper,the power transmission problem of a multi-core cable is abstracted into a multi-conductor transmission problem.Based on this,a vertical multi-core cable used in the deep sea is modeled.This paper firstly uses the energy method,charge quantity method,Neumann formula method,and average potential method to deduce the expressions of the inductance and capacitance parameters of the multi-conductor system in detail,and introduces the positional relationship between the conductors,the influence of the seawater medium and the ocean depth in the parameter calculation,and then a specific model of a vertical multicore cable used in a deep-sea environment is obtained.Then,use Matlab to calculate the parameter matrix,and use EMTP’s branch calculation engine to assist the calculation of the response of various inputs.According to the model,the voltage and current response along the line under various excitation conditions can be calculated.Based on this,the voltage drop and loss along the 6km submarine cable used by the "Hailong" ROV system are analyzed under the power-on state,and solutions are provided for the phenomenon of the obvious voltage drop along the cable when the system power frequency is 400 Hz.Finally,the validity of the model is verified by comparison between experiments and simulations.