Introduction

The IEA/PICS ModHVC (International Scientific Research Program), managed by Dr Gilbert Teyssèdre (Senior Researcher at CNRS, Laboratory on Plasma and Energy Conversion –Laplace, Paul Sabatier University of Toulouse and CNRS) is developed in collaboration with Dr Thi Thu Nga Vu (Lecturer, Electric Power University, Hanoï Vietnam) and was awarded for the period 2018-2020.

CONTEXT AND OBJECTIVES

Energy transmission networks involving High Voltage Direct Current (HVDC) are currently being developed throughout the world notably for strengthening interconnection between existing networks and for connecting to distributed electrical energy sources issued notably from renewable energy (wind farms, solar power plants, etc.). Very often, part of these HVDC links are submarine or buried, requiring insulated cables. Polyethylene materials tend to be generalized for HV cable insulation due to processing ease. One of the key issues with these materials under DC stress is the prevention space charge accumulation, which represents an early failure mechanism for cables. Specifically, accessories like cable joints and terminations represent weak points in the cable, particularly as regards the hazardous field distribution resulting from the association of insulations of different nature. Indeed, the difficulty is raised by the resistive nature of the field distribution. The aim of this project is to provide modelling approaches of transient and steady state processes occurring in HVDC cable systems, with consideration of non-equilibrium thermal conditions on the cables.

RESEARCH PROJECT

The development of a reliable tool for anticipating stress endorsed by the system in service is a necessary step for the design of reliable energy links. A sensible point in these technologies when cables are involved is the joint between consecutive cable sections along with terminations of cables. A workshop has been organized (Sept. 2018) with broad audience at EPU in order to prospect for potential DC links in Vietnam and identify a relevant case study. The project aims at settling reliable model of the stress distribution in 200kV cable joints. The reliability of the model is based on 3 important aspects that are:

– The relevance of data characterizing materials being used. This encompasses the temperature and field dependence of the conductivity along with the thermal properties of materials;

– The form of the model, i.e. macroscopic electrical involving permittivity and resistivity vs. charge drift-diffusion model involving charge generation

– The implementation of relevant modeling tools. A commercial software based on finite element method will be used. Steady state stress as well as transient conditions, both electrically and thermally are considered.

institutions and laboratories involved

France
• Dr Gilbert Teyssèdre and Dr Séverine le Roy (Laboratoire Plasma et Conversion d’Energie – UMR 5213 CNRS-UPS-INP)

Vietnam
• Dr Thi Thu Nga Vu and Dr Tung Tran Anh (Electrical Power University Hanoï)

Temperature and field distributions after 3′ and 8h simulated in a cable joint while the cable is energized under a current of 1kA and a Voltage of 200kV. 

Crédits: Thi Thu Nga Vu