Dissolved gas analysis investigations on ester liquids after breakdown

Abstract

To offer more personal safety and a better environmental behavior of electrical power supply, the usage of alternative insulation fluids is demanded in large power transformers. The minimizing of fire loads is another significant reason for these new liquids. A number of companies are offering such alternative insulation fluids which are already used in distribution transformers but there is still little experience with those liquids in large power transformers. One reason for this is missing maintenance information like limit values of the different DGA detectable gasses. For mineral oil there are many different interpretation methods for DGA (Dissolved Gas Analysis) results and also many known patterns for specific reasons of the increase of one or more gas values. This investigation shows which gas values change significantly caused by breakdown in an oil/cellulose insulation system resp. an ester/cellulose system. A test setup was created and experiments were done with mineral oil, a natural ester and a synthetic ester. A DGA analysis was carried out before and after several breakdowns in the liquids. With the results the gasses which indicate an oil/cellulose breakdown could be identified.