Anomalous oil electrification phenomena in Couette flow between bare stainless steel electrodes

Electrification, which occurs in transformers due to the entrainment of electrical double layer charge from the recirculatory flow of the oil over internal insulating pressboard surfaces, is simulated in an apparatus consisting of two coaxial cylinders filled with oil. The inner cylinder is rotated, resulting in a turbulent flow in the fluid region between the inner and outer cylinder. Measurements of oil charge density, open circuit voltage and short circuit current are made. Experiments using bare stainless steel cylinders demonstrate transient behavior having time constants which are much greater than known time constants of the oil dielectric. Anomalous and nonreproducible system responses occurring due to changes in rotational speed, as a result of electrical prestressing, and for no known reasons are observed