hello, i had a merlin gerin 5 kva 31 series model ups for 3 phase to 1 phase. the arrangement from company manual said that the optional isolation transformer shall be at output side of ups it means a single phase 1:1 ratio xformer at ups output but by some ignorance i had a design as a
3:3 phase isolation Xformer at UPS input. The fuses inside ups are
10amp per phase and the battery is connected externally to have greater
back up times and charged by external charger which takes three phase input from primary of isolation Xformer. Odd enough!
the transfomrer burnt and this has to be investigated. the indications on ups diagnostics were unit was on static bypass units mains fuses were blown (we found r and b phase fuses were blown) units internal charger orand rectifier is/are damaged(internal charger was disabled i dont know how but internal ups battery and charger can support up to 8 mins so were disconneced by local supplier and this external battery with charger were added, battery was 60 amps each total 180 volts etc 12 * 15 may be) my Ac input is 440 volts delta and 230 volts in phase Neutral 50 hz. isolation Xformer is delta to star. the meger test showed insulation failure in Y phase for the Xformer primary and secondary. Dhananjay