Effects of particle size and concentration on the pulsation characteristics of transformer oil

The presence of particulate matter in oil has a great impact on the pulsation characteristics of oil. The effects of particle size and concentration on the pulsation characteristics of oil were studied to ensure the safe operation of oil equipment. According to the ISO 4406 standard for oil contamination, oil samples containing Cu, Fe, and SiO2 with particle sizes of 5, 15, 25, and 50 mu m and concentrations of 6.58, 4.57, 3.00, 0.971, 0.648 ppm were configured. Oil flow with different particle sizes and concentrations was tested in a square tube using PIV measurement technology. The instantaneous velocity vector data of the flow field were acquired in oil with different sizes and concentrations of the particles, and the distributions of the pulsation intensity of oil along the streamwise and normal directions were analysed. The time-frequency curves of the transient velocity and average velocity were discussed. The results showed that the distribution of the streamwise pulsation intensity of oil changes more gently along the normal direction in the centre region and changes more steeply in the near-wall area. With increasing particle concentration, the streamwise pulsation intensity of oil decreases gradually. The distribution of the normal pulsation intensity of oil along the normal direction is rough `w'-shaped under different particle diameters. With increasing particle concentration, the main frequency trend of the oil speed along with the streamwise and normal directions decreases, and the streamwise average speed of the oil increases. The change in the normal average speed of oil decreases when the particle concentration is under 3.00 ppm. The normal velocity of oil increases when the particle concentration is over 3.00 ppm.