Numerical Study of Heat Transfer in Trefoil Buried Cable with Fluidized Thermal Backfill and Laying Parameter Optimization

Chen-Zhao Fu,Wen-Rong Si,Jian Yang,Lei Quan

doi:10.1155/2019/4741871

Abstract

Trefoil buried cable is one of the important cable arrangements for the underground transmission line, and its heat transfer performance is relatively poor. By filling with fluidized thermal backfill material (FTB) around trefoil buried cables, the heat transfer would be efficiently enhanced, while the filling cost should also be considered. In the present study, the heat transfer process in the FTB trefoil buried cables is numerically studied, where the cable core loss and eddy current loss in the cable were coupled for the simulation. The heat transfer performances and ampacities for trefoil buried cables with different back fill materials were analysed and compared with each other. Then, the laying parameters for the parabolic-type FTB trefoil buried cables were optimized with the radial basis function neural network (RBNN) and genetic algorithm (GA). Firstly, it is found that, with FTB material, the maximum temperature in the cable core is obviously reduced, and the cable ampacity is greatly improved as compared with the cables buried around natural soil (NS). Secondly, when compared with flat-type FTB model, the heat transfer rate in the cable with parabolic-type FTB laying method would be slightly reduced, while the FTB amount used for the buried cables is greatly reduced. Finally, as for parabolic-type FTB trefoil buried cables, with proper design of geometric parameters (s1 = 0.290 m, s2 = 0.302 m, and l = 0.3 m with I = 1300 A) for the FTB laying cross section, the overall performance for the cable was optimized.

Highlights

As global economics increases, the demand for electricity supply increases rapidly [1]
The heat transfer process in the fluidized thermal backfill material (FTB) trefoil buried cables is numerically studied, where the cable core loss and eddy current loss in the cable were coupled for the simulation
The laying parameters for the cross section of parabolic-type FTB trefoil buried cables were optimized with the radial basis function neural network (RBNN) and genetic algorithm (GA), and the optimum laying parameters and minimum total cost function were obtained

Summary

Introduction

The demand for electricity supply increases rapidly [1]. The surrounding soil near the buried cable will be heated and the soil will become dryer. This will drastically reduce the soil conductivity and directly affect the heat transfer in the cable system [4, 5]. In order to avoid soil desiccation and overheating of cables, the fluidized thermal backfill material (FTB) would be filled around the cables, which would efficiently improve heat transfer rate for the buried cable system [6]. When the FTB laying method is used, heat transfer process in the cable system should be investigated, but the laying parameters should be optimized to reduce the FTB laying cost

Methods

Results

Conclusion