properties of mineral insulating oils in service

the infrastructure of the electricity grid and super grid system in the hitherto industrialized world was to a large extent built up in the decades following world war ii with a peak in investments around 1960-1980. this means that the flotilla of power transformers is now starting to reach projected lifetime of around 40 years. during the last couple of decades there has also been an ongoing deregulation and privatization of electricity generation and distribution. this has led to higher utilization of existing equipment to deliver an ever increasing demand of power. the demand for planned asset management, investments, reliability and availability of power delivery, has also increased. to ensure that aging equipment is working satisfactory and will do so for yet some time, interest in aging behavior of power equipment has increased. yet there is precious little basic information openly available on how the insulating materials in transformers behave over longer periods of time. such information is valuable both from the perspective of transformer maintenance/asset management, and as background information to make informed choices on which type of insulating liquid to employ in new equipment.