Testing of breakdown voltage of transformer oil - test assembly preparation
IEC 156 automatic BDV test kit
It is recommended that a separate test cell assembly be reserved for each insulating liquid type.

Test assemblies shall be stored in a dry place, covered and filled with dry insulating liquid of the type in regular use in the cell.

On change of the type of liquid under test, remove all residues of the previous liquid with an appropriate solvent, rinse the assembly with clean, dry liquid of the same type as that to be tested, drain and refill.