1. History of insulating liquids in electrical engineering

The first insulating liquid proposed for application in power transformers was patented in the USA in 1887, followed in 1891 by a British patent . This first mineral oil-based application was first used in 1892. Initially, oils were obtained from paraffinic bases. Around 1925, naphthenic mineral oils were also introduced. Additives were gradually added (antioxidants, pour point improvers, etc.). Over the years, various types of insulating fluids have been used...