Characteristics of elastic waves caused by corona discharges in an oil-immersed pole transformer

Measurements of elastic waves brought by a pulse of simulated corona discharge in an oil immersed pole transformer and a model tank filled with oil were performed in order to identify the location of insulation deterioration, using an acoustic emission (AE) technique. The detected AE signals were analyzed by means of a fast Fourier transform (FFT), and properties of elastic waves influenced by the existence of insulated windings and magnetic core for power transformation in the transformer were investigated. The result shows that almost all the initial AE signals detected on the-wall of the transformer tank were Lamb waves caused by the oscillation waves passing through the insulating paper and oil with repeating transmission, reflection and refraction. Also, it was possible to recognize whether the measured elastic wave was influenced by windings and their insulating papers or not, by FFT analysis. This suggests that the location accuracy of the corona discharge in the transformers would be improved.