HVDC XLPE 케이블 및 케이블 접속함의 정상상태 운전 중 개폐충격파 중첩에 대한 연구

Abstract

In recent years the increasing industrialization and growth in population has led to the increased demand of electricity. This has resulted in the increased stress on the conventional power transmission system and most existing AC transmission systems are approaching their thermal capability limits. HVDC transmission systems have emerged as a preferred solution for meeting the increased power transmission requirements over long distances. HVDC transmission systems incur low transmission losses, require smaller right of way and due to their controllability they can assist the existing AC grid and prevent major anticipated outages. A critical bottleneck in implementation of High Voltage DC transmission systems is the unavailability of insulation design technology. The major vendors of HVDC systems have not disclosed the DC insulation design technology so indigenous research and development efforts must be carried out in this area. For the insulation design of dc apparatus, dc electric field analysis should be carried out to figure out electric field distribution and find the locations of concentrated electric field and electric field intensities under steady state and transient circumstances. Switching Impulse is known to cause high level of superimposed EMF and as a result the electrical field intensities. SI has hence the high probability to cause the breakdown of insulation. Therefore a detailed analysis of superimposed Switching Impulse has been carried out. In this thesis, the simulation studies were carried out using COMSOL Multiphysics for analyzing dc electric field under steady state in XLPE cable and outdoor termination. And then, we performed the simulations to compare two cases of switching impulse superposition i.e. positive and negative switching impulse on positive dc steady state. In addition, to evaluate insulation performance of XLPE specimen dielectric breakdown test of switching impulse superposition was performed. Finally, FGM was applied for electrical stress control in the outdoor termination. As a result, the effect of field relaxation was verified by application of FGM. Through this study, it will be possible to acquire the dc insulation design technology under the condition of superimposed switching impulse.