An ultrasonic signal propagation model of transformer partial discharge considering nonlinear attenuation in the temperature gradient field

In the actual operation of the transformer, the temperature rise characteristic inside the transformer presents a gradient distribution, which increases the temperature difference in the vertical direction inside the transformer, resulting in the increase of the difference in sound velocity due to the influence of temperature, and then brings certain errors to the positioning of the partial discharge source. Therefore, in order to obtain more accurate partial discharge ultrasonic signals, an ultrasonic signals transmission model of transformer partial discharge considering nonlinear attenuation in temperature gradient field is established. The internal temperature characteristics of the transformer under different load factors and the propagation characteristics of the ultrasonic signal under different load factors were analyzed. In order to analyze the propagation characteristics of ultrasonic signals under different load factors, we also proposed the frequency at the point of maximum sound pressure and the frequency range at 1/3 of maximum sound pressure as characteristic parameters to characterize ultrasonic signals. The results show that with the increase of winding temperature, the sound pressure amplitude decreases gradually, and the frequency gradually shifts from high frequency to low frequency. Therefore, it is necessary to carry out temperature correction for ultrasonic signal. This paper provides a theoretical basis for the ultrasonic localization of partial discharge in transformers.