The ultra-high frequency (UHF) method has been widely used in a gas-insulated system (GIS) for partial-discharge detection, and many achievements have been realised. In addition, many studies based on artificial defects have been made to confirm its validity. Therefore, the UHF method is generally believed to be sufficiently effective for GIS monitoring. However, in practical application, the authors find that for some micro-crack discharge in GIS insulator, the UHF method has low sensitivity. To fully study the characteristics of the micro-crack discharge in the GIS insulator, an experiment is conducted in this study using an actual post insulator with a micro-crack defect. The current signal based on IEC 60270 standard and the radio-frequency electromagnetic signal is simultaneously measured for thorough analysis. The results show that some submillimetre crack defects may occur in the GIS insulator. Its discharge is mainly presented as glow discharge, and the discharge signal frequency usually cannot reach the UHF band; thus, it cannot be effectively detected by the UHF method. This study provides complementary information to the applicability of the UHF method and inspires further study of the GIS insulator and its monitoring technology.

超高频（UHF）方法已被广泛用于气体绝缘系统（GIS）中以进行局部放电检测，并且已经取得了许多成就。另外，已经进行了许多基于人工缺陷的研究以证实其有效性。因此，通常认为UHF方法对于GIS监视是足够有效的。然而，在实际应用中，作者发现对于GIS绝缘子中的一些微裂纹放电，UHF方法灵敏度较低。为了充分研究GIS绝缘子中的微裂纹放电特性，本研究使用实际的具有微裂纹缺陷的后绝缘子进行了实验。同时测量基于IEC 60270标准的电流信号和射频电磁信号，以进行全面分析。结果表明，GIS绝缘子可能会出现亚毫米级的裂纹缺陷。它的放电主要表现为辉光放电，并且放电信号频率通常不能达到UHF频段。因此，UHF方法无法有效检测到它。这项研究为UHF方法的适用性提供了补充信息，并激发了对GIS绝缘子及其监测技术的进一步研究。