CONDITION DIAGNOSING

The present invention discloses a method and apparatus (5) for condition diagnosing of an inductive power device (1), such as a transformer or reactor, having power windings (2) immersed in a fluid (3) being cooled by cooling devices (4). The diagnosing method basically compares and evaluates expected heat flows into and out from the inductive power device (1) system together with an actual and a previous heat content of such a system. From the heat flows the heat balance in the system may be obtained and is used for diagnosing the operation conditions of the inductive power device (1). The results from the condition diagnosing may be used as indicators (70) that can alarm operators, may be sent as a data signal (80) to remote and/or portable display means (85), such as a computer, or may be used as input data to control or simulation systems.