Monitoring of power transformers using the transfer function method

The transfer function concept is well known as an additional method of evaluating the impulse test of power transformers in the test laboratory, Another application for this method is monitoring of power transformers in service. According to the method of how to measure transient signals for the calculation of transfer functions, two kinds of monitoring can be distinguished: off-line and on-line monitoring. Both kinds of monitoring as well as their influencing factors are discussed with on-site measurements on power transformers in service