1.1 This standard describes two test methods, A and B, for assessing the electric strength of insulating liquids in a divergent field when subjected to standard lightning impulse. Method A is based on a step procedure intended to provide an estimate of impulse breakdown voltage under specific conditions. Method B is a statistical test designed to check an hypothesis about the impulse breakdown probability of an insulating liquid at a given voltage level. 1.2 Both methods can be applied to unused or used insulating liquids, the viscosity of which is lower than 700 mm2/s at 40 °C. The methods can be used with positive or negative impulses. No specific stipulations are made regarding the preparation of the liquid sample provided that it corresponds to industrial practice; however, tests made before and after treatment of the sample may be useful for demonstrating the effect of treatment. 1.3 Both methods are primarily intended to establish standardized procedures for assessing the impulse electric strength of insulating liquids. They may serve to differentiate dielectric liquids between each other and to detect variations in their characteristics due to modifications in their chemical composition as the result of changes in the manufacturing process and/or feed-stocks.