This paper presents experimental results of the performance of two types of electrostatic filter for insulating liquids that utilize both AC and DC electric fields. The filters are cylindrical in shape and consist of a coagulating part, in which an AC electric field is applied to make minute contaminant particles become coagulated, and of a capturing part, in which a DC electric field is applied to capture the particles. The sole difference in the two types of filter is in the magnitude of the velocity gradient in the passage of the coagulating part. It is shown that the filtration speed is increased by utilizing both AC and DC electric fields compared to the case where only the DC electric field is used, and the usefulness of the electrostatic liquid filter proposed is demonstrated. Comparison between the performance of the two types of filter shows that the magnitude of the velocity gradient in the passage of the coagulating part strongly affects the filtration speed.
