Study on the Charge Calculation and Influencing Factors of Metal Particle Groups in Fluid-Electric Coupling Field

In the life cycle of power equipment, the insulating oil is easy to mix with various solid impurity particles such as metal and fiber, which will cause electric field distortion and insulation balance failure of equipment. Therefore, considering that compared with non-metallic particles, metal particles have a greater impact on partial discharge and arc breakdown of oil, this paper proposes a method to derive the charge of particles by analyzing the force model of metal particles on the basis of discrete particle model, and reveals the influence of electric field intensity, voltage type and flow velocity on the charge distribution of metal particles. Firstly, the internal oil channel environment of power transformer was simulated and the experimental observation platform for particles in oil was built. Secondly, the force model of metal particles in the fluid electric coupling system was established combined with fluid dynamics. The formula for calculating the charge of metal particles under experimental conditions was derived through the formula. Thirdly, the particle image velocimetry (PIV) system was used to capture the cloud picture of particle swarm velocity and streamline, and the velocity and acceleration of metal particles were calculated through the streamline of particles and the finite difference method, so as to calculate the charge of particles, which was close to the charge of particles calculated by the traditional model. Finally, by changing the applied voltage, oil flow rate and voltage type, the charge value and distribution of metal particles in the oil flow were calculated and counted. The experimental results show that when the flow rate of insulating oil is 0.15 m/s, the maximum charge of particles is 0.17 pC, and the proportion of particles with the absolute value of charge greater than 0.01 pC is 36%, while when the flow rate is 0.3 m/s, the maximum charge of particles is −0.13 pC, and the proportion of particles with the absolute value of charge greater than 0.01 pC is 29%, which may be due to the increase of horizontal drag force on particles when the flow rate of oil increases. The time of particles flowing through the electric field region is shortened. When the voltage is −10 kV, the maximum charge of particles is 0.05 pC, and the proportion of particles whose absolute value of charge is greater than 0.01 pC is 12%. When the voltage is −20 kV, the maximum charge of particles is 0.09 pC, and the proportion of particles whose absolute value of charge is greater than 0.01pC is 25%. When the voltage is −30 kV, the maximum charge of particles is 0.17 pC, and the proportion of particles whose absolute value of charge is greater than 0.01 pC is 36%. The acceptable explanation is that the increase of electric field intensity leads to the increase of collision probability between particles and electrodes. When the applied voltage is AC, the proportion of particles with the absolute value of charge greater than 0.01 pC is about 10%, and the maximum charge of particles is 0.03 pC. Through the above analysis, it can be concluded that: (1) The maximum charge of particles is in the same order of magnitude as the traditional model, but the distribution curve of the charge proportion of particles is close to the Gaussian distribution. (2) With the increase of insulating oil flow rate, the movement time of particles in the electric field between electrodes is reduced, resulting in the reduction of the probability of particles colliding with electrodes in the same time interval, and the proportion of particles not colliding with electrodes is increased. (3) The velocity component of particles in the vertical direction increases, the collision between particles and electrodes becomes frequent, and the charge of particles generally increases. (4) When the applied voltage is AC, the particles with large charge account for less. © 2024 China Machine Press. All rights reserved.