Vibration diagnostic method of large power transformers

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Janka Sándor
Department of Electric Power Engineering

The thesis is about how to perform the measurement of the transmission and distributor electrical network's power transformers' vibration diagnostics. The active part of the transformer is built of windings and iron core. The windings vibrate because of the force generated by the coil currents. The iron core vibrates too because of the force generated by the magnetic flux induced by the coil currents. The active part is propped to prevent being moved by the vibration. However if any failure should happen in these units it could be detected from the vibration's spectrum so the condition of the transformer can be monitored without being turned off. This way there is no need to interrupt the continuity of the power supply.

The object of the thesis is to measure and record the data required to calculate and plot the spectrum and produce a measurement number from the data. This number gives a feedback about the transformer's condition. The aim is to monitor this number online with a computer and if it exceeds a threshold the system sends a message about the required maintenance or turns the transformer off if needed.

The first chapter of the thesis reviews the operation and physical bases of the transformer especially from the mechanical vibrations' formation's aspect. The measured transformer's power is 75 kVA and it's voltage transmission ratio is 380//174/130/152 V. The 380/174 V ratio is used for measurement. The second chapter reviews the theoretical possibilities of the vibration measurement then it selects the most appropriate method for it. The used accelerometer's construction, structure and physical bases are presented. The third chapter describes the PC-fit measurement card which makes the accelerometers' signs processable for the computer and presents the programs used for the measurement. These are made in LabVIEW and Microsoft Excel. The fourth chapter presents the measurement arrangement at the pillars' measurement in open circuit depending on the voltage. The next chapter describes the exact course of measurement explaining the results. The last chapter is about the development and real-world application possibilities.


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