Novel charge generation model for simulation of streaming current based on shearing stress at the oil/pressboard interface

Although the streaming electrification phenomenon in oil-filled transformers has been studied intensively since the 1970’s, no simulation model or quantitative computation method is yet available for the streaming current, i.e. the electrical current caused by streaming electrification. We propose a novel charge generation model which makes it possible to numerically calculate the streaming current. In our model, oil flow velocity at the interface is approximated by the shearing stress at the oil/pressboard interface, which is an essential parameter in fluid dynamics. Combining the approximated velocity of the oil with the Debye model for positive charge distribution, we derive that the local streaming current is proportional to the shearing stress. Measured streaming currents were found to be proportional to the calculated shearing force for different duct structures and for different oil flow velocities, showing that the proposed model can be used to estimate the streaming current for a given duct structure in an oil-filled transformer.