A versatile three-terminal test cell for dielectric measurements on insulating liquids

A versatile three-terminal test cell is described that permits accurate determination of the relative permittivity and loss factor of liquids. The cell takes a small charge, complies with IEC publication 247, and is particularly easy to dismantle, clean, and use. it is simple to set up because its housing fits directly into the opening in a commercial oil bath. Electrode and sample temperatures are accurately monitored with thermocouples and a platinum resistance thermometer, none of which introduces electrical noise into the measuring system. With direct injection, relative permittivity measurements can be made to within ±0.00006%, this being twice the uncertainty in the air capacitance of the cell. The cell and its contents can be heated at a variety of rates, which makes it ideal for studying temperature-dependent loss in insulating liquids. Experimental results on a silicon fluid and high-voltage cable oil are included