Ricerc@Sapienza

The 2016-2018 ongoing revision of the lEC 60156 'Insulating liquids - Determination of the breakdown voltage at power frequency' was just approved and the revised standard will be published by the end of 2018. This document will include the recommended use of a stirring system with the main purpose to reduce the scatter in the ac breakdown voltage results. The present paper reports a comparison of breakdown voltage mean values and related scatters of two different insulating liquids (traditional mineral oils and natural ester liquids) in accordance with the tests methods of the actual and 2018 upcoming revision of IEC 60156. The results presented here confirm that the modification (stirring system) introduced in the lEC standardized test method, even a simple rearrangement, is able to reduce the scatter of the mean values of the breakdown voltage of the insulating liquids. Some considerations of an alternative test method procedure introduced by the 2018 upcoming revision of lEC 60156 are also reported. © 2018 IEEE.