Evaluation of Electrical Characteristics on HVDC Cable According to Electric Field Dependency

The electrical conductivity of an insulation material is a dominant factor that determines a dc electric field distribution, and it depends on temperature and electric field intensity. It is generally known that the electrical conductivity of an insulation material is more influenced by temperature than the electric field intensity. Thus, the electric field analysis method of the dc cable excluding electric field dependency may be suitable for LVDC and MVDC power cables. However, high intensity electric field occurs in HVDC voltage levels, which greatly affects the change of electrical conductivity of the insulation material. Thus, unless the electric field dependency is taken into consideration in electric field analysis for HVDC cables, the accuracy of field distribution is lowered. In this study, dc electric field analysis according to field dependency coefficient was performed in order to investigate an influence of electric field dependency of electrical conductivity on dc field distribution. We also considered an effect of temperature gradient and voltage level to obtain the accurate result of electric field analysis under various operation conditions. As a result, electric field intensity on conductor side was largely increased, whereas electric field intensity on sheath side was slightly decreased, compared with the case where the electric field dependency was not considered. In addition, when the field dependency coefficient of electrical conductivity increased, the rate of change of electric field distribution on the conductor side was larger than the sheath side. As the temperature gradient and voltage level increased, the variation of the electric field distribution with application of the field dependency coefficient increased.

I. Introduction

Due to the rapid growth of renewable energy, it is possible to generate electricity in various ways such as offshore wind power and solar power generation, and the location of power plants are becoming diverse [1 – 2] . Also, with the progress of inter country power grid connection, worldwide interest in long distance power transmission is increasing [2] . The HVDC cables used for long distance power transmission demands a higher voltage and higher capacity. Therefore, development of power cables applicable to the HVDC environment is actively being carried out. Proper insulation design and reliability for HVDC cable should be ensured before commercialization and stable operation [3] . The dc electric field characteristics are significantly different compare to ac. The electric field distribution of the ac cable depends on the permittivity. However, the electric field distribution of the dc cable is determined by the electrical conductivity of the insulation material [4] .