How to Measure the Dielectric loss of 500kV Circuit-breaker Capacitor at High Voltage

Abstract: Measurement of capacitance and dielectric loss of circuit-breaker capacitor is a very important task to ensure safe and stable running of circuit-breaker. However, due to serious electric interference to on-site measurement, dielectric losses of more and more 500kV circuit-breaker capacitor exceeded the limit at 10kV test voltage according to the CSG trial standard. To address the above-mentioned problems, the paper proposes that methods of using different frequency power source and boosting test voltage be utilized to measure the capacitance and dielectric loss. Based on the above measuring methods, several common test schemes are put forward and  application ranges are also analyzed followed by capacitance and dielectric loss measurement for some 500kV circuit-breaker capacitor at Liu-dong substation. Test results indicate that the dielectric loss of capacitor reduces as the voltage rises; the change in test voltage frequency can effectively shield the interference from on-site electric field.   

Key words: 500kV, circuit-breaker capacitor, capacitance, dielectric loss, high voltage, measurement        

Introduction

During the process of capacitance and dielectric loss measurement, due to coupling capacitance between test object and surrounding live parts, the measurement is disturbed by electric field so that real capacitance and dielectric loss cannot be obtained. In addition, according to related test standard, the test should use 10kV test voltage. However, with the improvement of voltage level, the dielectric loss data at 10kV always fails to reflect the conditions of equipment during the operation. To address the above-mentioned problem, the paper proposes that methods of using different frequency power source and boosting test voltage be utilized to measure the capacitance and dielectric loss.