Frequency response analysis and insulation resistance measurement

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Cselkó Richárd
Department of Electric Power Engineering


The modern power transmission and distribution network depends on very expensive units of power transformers to provide power to consumers around the world. Correct application of diagnostic technologies is key to preventing any unwanted failure of the already aging fleet of transformers in the networks.

The purpose of this thesis project is an in depth study of the Frequency Response Analysis (FRA) and Insulation Resistance Measurement (IRM) diagnostic methods and how they are applied on power transformers, with the goal of keeping them in reliable operation and to prevent unforeseen failure events by recommending maintenance operations when necessary.

The thesis project report includes a theoretical description of the IRM and FRA diagnostic methods and a comparative analysis between them with emphasis on the kinds of defects they are able to detect.

The knowledge gained during the course of this project was applied by performing the FRA and IRM diagnostics on power transformers with an analysis and interpretation of the measurement results.

In the comparison of the two diagnostic methods, it was clearly stated that the FRA method detects any kinds of defects that cause geometrical changes from the original form of the equipment, while the IRM diagnostic methods detects irregularities which causes more current to be drawn by the insulating materials of the equipment under test.

As an experimental application of the diagnostic methods, two 3-phase transformers were tested using the insulation resistance measurement technique, while one 3-phase transformer was tested using the frequency response analysis method. The measurement results were analyzed using both graphical and numerical statistical models generated using the Microsoft excel computational software.

As a conclusion it was shown that the Frequency response analysis (FRA) diagnostic technique is a very sensitive and powerful method of detecting winding deformations and core movements in power transformers, where as the Insulation Resistance Measurement (IRM) diagnostic technique gives valuable information on the general condition of transformers based on the condition of the insulating materials, an appropriate diagnostic test to be performed as a preliminary preparation for other tests such as the dielectric test on power transformers [11].


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