Influence of AC and DC fields on streaming electrification of transformer oil

A study conducted by flowing transformer oil through a coaxial cylinder system is discussed. In the case of AC voltage, the streaming current increases with the field strength and with temperature. The increase of the streaming current at low AC field strength is attributed to vibration of positive ions, diffused into the oil at the interface with the electrode. In the case of DC voltage application, the polarity of the streaming current varies from slightly positive at low DC field strength to negative at high field strength. The streaming current at low fields may be caused by the difference between positive and negative ion mobilities.>