Development and Application of Compact Type On-line PD System at on-site for detecting PD by applying AC withstand voltage in underground power cable

摘要

Extra high voltage underground power cable (UGC) is critical to establish backbone grid network and its economical and social effect is strongly immense in case of faults. In this regard, since more than three decades, Partial Discharge (PD) measurement has become accepted as one of the effective method to diagnose. In order to carry out PD test for commissioning test, recently, portable PD measurement has been introduced during applying nominal voltage after completing AC withstand test. However, this conventional method lacks reliability in terms of detecting irregularly and inadequately repeated PD signal; indeed, this method is not able to detect PD occurrence during AC withstand test owing to the security problems. For this reason, the compact type PD monitoring system has been developed to assure cable performance in case of applying initial voltage, and has been introduced on commissioning test for 345 kV underground cables in actual grid. In this study, this system shows several advantages comparing with the conventional one as follows; higher possibility to detect PD signal comparing with conventional one by carrying out PD test during commissioning test: Applying AC withstand voltage for PD test, i.e. 250kV in 1 hour for 345 kV UGC. Improvement of the reliability to increase accuracy to analyze PD signal by introducing frequency analysis, pulse analysis and time difference analysis, simultaneously In accordance with the statistical result, the failure rate of XLPE cable is over 50% within 1 year after commissioning. Accordingly, it is able to provide the solution for reducing initial failure and for analyzing fault parameter of XLPE cable by carrying out AC withstand test and PD test at the same time. Furthermore this compact type PD monitoring system is able to provide cost reduction against installation cost of the conventional PD system. Direct connection between UGC monitoring system and this system is another advantage to monitor PD performance in actual grid.