Impact of furan analysis on asset management of high voltaga transformers in the Belgian transmission network

One of the most reliable indicators today to assess the paper insulation system of power transformers in service, is the measurement of the concentration of furan compounds in the insulation oil. The determination of the content of 2-furfuraldehyde, 2FAL, is done by chemical laboratory analysis on oil samples taken from the transformers. Based on these results, the Belgian Transmission System Operator categorises the assessed transformer into one out of four different "furan classes". These classes, solely based on the furan content of the oil sample, define the different actions and provisions to be taken in order to improve overall grid reliability. The 2FAL content measurement is a standard analysis performed in the laboratory, but gives only an indication of the life consumption of the transformer. Many factors influence the formation of 2FAL and its correlation with the average degree of polymerisation (DP) depends on several transformer characteristics. It is therefore unusual to take direct replacement actions only based on these measurements when the 2FAL concentration is too high. Instead, the furan classification divides the power transformer assets into different levels of risk of failure related to the insulation system condition. For each class, a specific set of curative actions and measures are defined. The classes are numbered 1 to 4, with class 1 the class with the lowest concentrations. As most of the transformers reside in this class, the only action to be taken is the follow-up of the 2FAL content on a regular basis. When the transformer is categorised in one of the higher classes, the normal exploitation of the substation will be altered to minimise the impact of the concerned power transformer on the grid. Other measures that are to be taken can be the obligatory replacement and scrapping, the prohibition of transportation to another substation, or the extension of the spare transformer assets. The 2FAL content in the insulation oil of all transformers are assessed in order to discover the units at risk in the grid. Based on this classification, the Belgian Transmission System Operator changed with success its transformer asset management: five years ago a strategic forecast was established and a replacement program was initiated for the power transformers in the highest class. In addition, the classification served also as one of the steering factors to define a new spare transformer purchase policy. Over the years, the number of cri