GIS partial discharge quantitative measurements using UHF microstrip antenna sensors

In view of the structure characteristic and operation performance of the field gas insulation switchgear (GIS), an external ultra high frequency (UHF) sensor, a novel microstrip antenna, is designed to detect UHF partial discharge (PD) signals for the field GIS. The microstrip antenna, which receives the UHF electromagnetic wave leaked from the GIS spacer, is just mounted on the GIS spacer, and has some effect to suppress the surrounding space electromagnetic interference. The analysis and on-site measurements manifest that the microstrip antenna working frequency bandwidth is 340MHz to 440MHz, which voltage standing-wave ratio (VSWR) is less than 2, the center frequency is 390MHz, the relative bandwidth is 25.6% up to the wide bandwidth range, and its gain of the maximum radiation and reception directivity is covered 5.38dBi. Based on the laboratory GIS simulation device measurements, the investigation of the relationship between UHF PD amplitude and apparent discharge quantity based on IEC60270 is presented as linear curve. Meanwhile, comparison to the field 220kV level GIS, the quantitative charge evaluated to about 40pC by the UHF method could give a preliminary diagnosis for GIS insulation conditions. And the UHF measurement system is suited for GIS field partial discharge UHF on line detection and diagnosis.