The formulation of models for the description of streaming electrification in transformer structures

The incidence of streaming electrification in large transformers (and other industrial equipment) has generated the need for both an understanding of the underlying physics and a mathematical description of the phenomenon. Modeling is needed since the mechanisms do not readily scale and small-scale laboratory experiments are limited in predicting performance. The development of both steady-state and transient descriptions of the streaming electrification process is described for a rectangular duct structure. The nature of the phenomenon is such that appropriate assumptions and approximations need to be made. As a consequence, some experimental verification of the outcomes, at least in qualitative form, is also included. The entrainment of charge from the interface charge layers also intimately involves the flow of the liquid. A description of the flow regimes and a transient solution of the charge development through a duct are thus an integral part of the modeling effort. The utility of the steady-state model developed is demonstrated by application to an oil-cellulose system typical of a large core-form transformer. The method advocated takes advantage of the repeat duct arrangement in such units. The results presented allow the internal behavior of such a unit to be studied in considerable depth, and provide insight into the complex interplay between generation and relaxation in circumstances when flow rates, temperature, external fields and influent charge are changed.