• Rajko Gardijan
  • Alen Keller



power transformer, bushing, measuring tap, on-line monitoring, test


Power transformer is one of the most important and most expensive components in the electric power system (EPS) and requires, from its production and throughout lifetime, continuous monitoring and checks of the availability in the power system. All the measurements and tests on the transformer which manufacturers attempt, in order to determine the quality of their products, are carried out through the connection of different types of bushings, and these measurements and tests are conducted in accordance with requirements of applicable standards. Also, the owner of the transformer during the exploitation phase wishes and needs to know the status and availability of transformers for future work. The only available points of the transformer inside are the bushings. The technical practice from the early beginnings of the transformers are periodic off-line measurements. Following that practice and experience, the need arose for continuous supervision of transformer operation (on-line). In the 90’s the first simple systems for the transformer on-line monitoring appeared. Today, it is an established fact that the modern systems for on-line monitoring of transformers provide a complete insight in the transformer state including alarms in the case of critical states. It is realistic to expect in the future that these same systems, apart from providing diagnostics and giving alarms, will be authorized to switch off transformers in the case of necessity with high degree of confidence. An important role in on-line monitoring, as a part of measurement system, has a transformer bushing. For the purpose of both off-line and on-line measurements, manufacturers of the bushings are equipping them with the measuring tap. Unfortunately, despite intentions to standardize the components of the power system, this is not the case with the measuring tap, and the intention of this paper is to draw attention to these problems and to try to find a solution.


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