Streaming electrification dynamics in the multilayer sensor

Streaming electrification dynamics is experimentally investigated by using a multilayer sensor in a closed loop and fresh transformer oil. This sensor consists of two identical rectangular oil ducts constructed by pressboard paper and separated by a middle copper plane electrode. The ground current from this middle electrode is measured. Two outer steel plane electrodes are connected together and used to measure the capacitive 'accumulation' current. The leakage currents at the sensor inlet and outlet, as well as the streaming current are also measured. The waveforms of these five currents together and oil temperature at the sensor inlet are simultaneously recorded for laminar flow and at controlled operating conditions; namely, oil temperature, mean flow velocity, humidity, and pressure. The results reveal that the all-recorded currents nonlinearly augment with oil temperature and linearly with oil-flow velocity. These results are interpreted in terms of shear stress, physicochemical reaction, the effect of streaming/floating potential on the electrical double layer (EDL), temperature-dependent oil properties, and introducing an expression of the streaming current. Calculations of accumulated charges on steel electrodes and the loating potential of the copper electrode at different oil-flow velocities, and the fully developed wall space-charge density and physicochemical reaction coefficient are presented.