Dielectric Breakdown Voltage Testing - Part 3

Technical Briefs

Dielectric Breakdown Voltage Testing Part 3 – ASTM D1816 for In-service Insulating Liquids - The History

In this article, we will continue our discussion of the standard methods for determining dielectric breakdown voltage. The subject is ASTM D1816, Dielectric Breakdown Voltage of Insulating Oils of Petroleum Origin Using VDE Electrodes. Although designated specifically for insulating oils of petroleum origins and limited in application to fluids of viscosity within certain parameters by the standard, D1816 has become much more widely used over the past several years.

De-emphasis of D877 and greater reliance on D1816 was accelerated by the revision in 2002 of IEEE Standard C57.106, Guide for the Acceptance and Maintenance of Insulating Oil in Equipment. D1816 is more sensitive to moisture in insulating oil, as well as to oil aging and oxidation. This determination is also more consistently affected by the presence of particles, particularly insulation fibers.

This standard method of measuring dielectric breakdown voltage uses spherical VDE (Verband Deutscher Elektrotechniker) electrodes. The method is run at one of two gap settings: 1 millimeter (0.04 inches) or 2 millimeters (0.08 inches). Because of the greater sensitivity, the rate of voltage rise is lower – 500 volts per second. Also, the D1816 test cell has a motor driven agitator. This agitator runs during the test to cause the oil to flow between the electrodes, carrying suspended particles into the gap between the VDE spheres where they can affect the breakdown voltage.

Originally, the method was intended strictly for equipment with a primary voltage class of 230 kV and above, where the oil had been processed with vacuum and filtration before being installed. Over the years, a number of labs began using the method to evaluate in-service oil from equipment of lower voltage classes, and the 2002 revision of IEEE Standard C57.106 incorporated D1816 limits for new and in-service oil. Since then, this method has been incorporated into standards for other fluids such as silicone and natural ester fluids.