The rapid growth of gas insulated switchgears as a compact, efficient, and reliable device has recently been given great attention. Albeit gas insulated switchgears can seldom suffer from failure due to the high resiliency and robustness, some severe damages have been experienced by such devices particularly in the event of partial discharge. Thus, monitoring such accidents has become a vital part of power systems reliability. The ultra-high frequency techniques have recently shown superior performance in the detection and classification of electromagnetic waves produced by partial discharge. This is mainly due to the great immunity to the noise of the ultra-high frequency detection techniques compared with the veryhigh-frequency counterparts. This review paper highlights the mathematical aspects of the electromagnetic waves generated by partial discharge. It also delivers an overview of the electromagnetic wave behavior in the complex structure of gas insulated switchgears, and outlines the important characteristics of the internal and external partial discharge detection using ultra-high frequency methods. INDEX TERMS Electromagnetic waves behavior, finite difference time domain, gas insulated switchgears, partial discharge, sensors, ultra-high frequency measurements.

Gas-insulated switchgears (GIS) have become essential parts of electrical power substations due to the associated merits of these capital assets. Although such resilient devices can rarely suffer from failure, partial discharge (PD) is responsible for around 85% of their recorded collapses. Ultra-high frequency (UHF) techniques have been widely used in the detection and localization of PD for a long time because of their immunity to noise and high sensitivity. Understanding electromagnetic (EM) wave behavior in GIS systems is significant for improving the utilization of UHF sensors in PD detection and for the optimal allocation of UHF antennas inside GIS systems. Thus, this paper is devoted to building a detailed 3D finite element (FE) model based on UHF detection techniques to understand the propagation behavior of EM waves inside GIS. A disk-type UHF sensor is used for acquiring EM waves inside the GIS. The sensitivity of the sensor has been obtained using a gigahertz transverse-electromagnetic (GTEM) test cell. The proposed model investigates the impact of multiple disconnecting parts including L-structure, relative angle between PD source and sensors, and disconnecting switches on the propagation of electromagnetic waves based on step 1 of the CIGRE recommendations. To validate the modeled GIS, a simple L-structured model is initially built, and a comparative analysis has been conducted between the built model and the experimental and analytical results from the literature.

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