Salvador Carvalhosa

Abstract
—The main objective of this work is to summarize the most commonly used dielectric fluids in the power distribution transformers, as well as to discuss what are the latest and the rationale behind those trends. The favorable and unfavorable reasons for any choice behind each of those dielectric fluids will be discussed. Additionally, this work also advances the power distribution transformers health index most commonly used to assess the condition of the transformer.

Abstract
Since the entry into service of the so-called Primary Network in 1951 until the 1960s, when the first electrical power interconnection between Portugal and Spain was created, that the Portuguese National Transmission Network could be considered a closed system, however, since the year 1961, that was no longer true. Taking these facts into account, the need to think and draw up new standards and regulations, with the widest possible coverage, has arisen in order to oblige European operators to maintain a level of control, security and knowledge of their transmission networks, which ensure that these do not influence each other negatively and that there is a coordinated response to incidents that may occur. © 2019 IEEE.