도전율 측정을 통한 DC 초전도 케이블의 과도 전계 특성 연구

Abstract

Recently, HVDC transmission system has been regarded as one of feasible solutions for upcoming super grid and transportation of renewable energy. Especially. DC superconducting system is considered as ideal case of HVDC. In order to design and develop HVDC power cable successfully, DC electric field distribution should be considered as a fundamental step of insulation design in various points of view. Insulation design of HVDC power equipment requires the knowledge of DC electric field distribution in order to optimize its insulation structure and size. Unlike AC electric field which only considers capacitive field, DC field analysis should include capacitive field, resistive field and also the mixture of resistive and capacitive field during transient state. And the DC transient state is the most important one to determine the performance of insulation design of DC power equipment. But, the DC electric field at transient state has been not fully investigated yet considering two main factors which affect the electric field distribution including the time constant and rate of voltage rise. In this paper, in order to evaluate the effect of those two factors on the DC electric field intensity at transient state, cylindrical double-layered dielectric model was analyzed which is essential design structure of DC superconducting cable both by mathematical formulas and DC electric field analysis by CAE tools. Then, by changing the time constants and rate of voltage rise, their effects on the DC electric field distribution during DC transient state were minutely examined. In addition, The electrical conductivity of PPLP specimen in LN2 was measured for the DC electric field distribution analysis for DC superconducting cable. Consequently, it was deduced that a dielectric material which has a larger time constant value shows a higher initial peak value of electric field intensity. And also field intensity has increased according to the increase of rate of voltage rise. Finally, it was suggested that the initial peak value of electric field intensity could be controlled by decreasing rate of voltage rise during the DC applying stages.