, ▁depending ▁on ▁econom ics , ▁transform er ▁duty ▁and ▁other ▁factors , ▁be ▁tested ▁period ically . ▁Power ▁utility ▁companies ▁have ▁a ▁v ested ▁interest ▁in ▁periodic ▁oil ▁testing ▁since ▁transform ers ▁represent ▁a ▁large ▁proportion ▁of ▁their ▁total ▁assets . ▁Through ▁such ▁testing , ▁transform ers ' ▁life ▁can ▁be ▁substantial ly ▁increased , ▁thus ▁delay ing ▁new ▁invest ment ▁of ▁replacement ▁transform er ▁assets . ▁ ▁On - site ▁testing ▁▁ ▁Rec ently ▁time - consum ing ▁testing ▁procedures ▁in ▁test ▁l abs ▁have ▁been ▁replaced ▁by ▁on - site ▁oil ▁testing ▁procedures . ▁There ▁are ▁various ▁manufact ur ers ▁of ▁port able ▁oil ▁test ers . ▁With ▁low ▁weight ▁devices ▁in ▁the ▁range ▁of ▁ 2 0 ▁to ▁ 4 0   kg , ▁tests ▁up ▁to ▁ 1 0 0   k V ▁r ms ▁can ▁be ▁performed ▁and ▁reported ▁on - site ▁automatically . ▁Some ▁of ▁them ▁are ▁even ▁battery - power ed ▁and ▁come ▁with ▁access ories . ▁ ▁Break down ▁voltage ▁testing ▁procedure ▁▁ ▁To ▁assess ▁the ▁ins ulating ▁property ▁of ▁die lect ric ▁transform er ▁oil , ▁a ▁sample ▁of ▁the ▁transform er ▁oil ▁is ▁taken ▁and ▁its ▁break down ▁voltage ▁is ▁measured . ▁The ▁lower ▁the ▁resulting ▁break down ▁voltage , ▁the ▁poor er ▁the ▁quality ▁of ▁the ▁transform er ▁oil . ▁▁ ▁The ▁transform er ▁oil ▁is ▁filled ▁in ▁the ▁vessel ▁of ▁the ▁testing ▁device . ▁Two ▁standard - comp li ant ▁test ▁electro des ▁with ▁a ▁typical ▁clear ance ▁of ▁