MINERAL INSULATING OILS IN SERVICE Monitoring and their properties

The infrastructure of the electricity grids 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 higher demand of power. The emand for planned asset management, investments and reliability of power delivery, has also increased. To ensure that aging equipment is working satisfactory and willdo 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 makeinformed choices on which type of insulating liquid to employ in new equipment. In this study there is a total of 145 separate oil samples from separate transformers (all samples appeared around the same time for analysis), of which 114 are inhibited and 31 uninhibited (as defined by IEC 60296) The inhibited oil samples, comparable to ASTM D3487 Type II, came from transformers in the Nordic region in Europe, whereas the uninhibited samples came mainly form the Middle East. The transformers span a range of ages from only a few years up to 45 years. The samples were analyzed for acidity (neutralization number), interfacial tension, dielectric loss (DDF or power factor) and peroxide content. The inhibited samples were also analyzed for inhibitor content. All of these parameters except peroxide content are standard measurements, but little information exists on how they relate to each other statistically. The peroxide measurements were performed according to a method we have developed. It should tell us more about the oxidation behavior and the efficiency of oxidation inhibitors.

MINERAL INSULATING OILS IN SERVICE Monitoring and their properties Keywords:

Transformer oil , inhibitor , oil oxidation , in-service oil , inhibitor to up