This book offers an insight into the insulation failures in GIS/GIL and provides practical guidance for improving the insulation reliability of epoxy-based spacers. High voltage gas-insulated apparatuses, including gas-insulated switchgears (GIS) and transmission lines (GIL), playing an important role in the global power transmission system. Epoxy-based spacers are key components in GIS/GIL, playing the role of electrical insulation and mechanical support. However, insulation failures frequently occur around the epoxy-based spacers, threatening the safe operation of the electric power...