Abstract:Because of the excellent performance of ferric phosphate lithium cells,it has been greatly applied to domestic power system. However,the substations who adopt ferric phosphate lithium cells just simply substitute lead - acid batteries with ferric phosphate lithium cell,it doesn't consider the charging and discharging characteristics of ferric phosphate lithium cells, and it will accelerate the capacity fading of ferric phosphate lithium cells and reduce its service life so as to cut down its performance /price ratio. In order to solve the problems as mentioned above,the non - floating method based on ferric phosphate lithium cell is studied for DC supply system in substation,that is,the batteries will not be supplied until needed by the charging device which is only for regular load in normal condition.