Understanding UPS Operation7-8 EATON Powerware® 9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev E powerware.com7.2.4 Battery Mode – RTThe UPS automatically transfers to Battery mode if a utility power outage occurs, or if theutility power does not conform to specified parameters. In Battery mode, the batteryprovides emergency DC power that the inverter converts to AC power.Figure 7-4 shows the path of electrical power through the UPS system when operating inBattery mode.StaticSwitchK5Rectifier InverterK1 K3BatteryConverterBatteryCB2Main Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers ContactorsFigure 7-4. Path of Current Through the UPS in Battery Mode – RTDuring a utility power failure, the rectifier no longer has an AC utility source from which tosupply the DC output current required to support the inverter. The input contactor K1opens and the battery instantaneously supplies energy to the battery converter. Theconverter either bucks or boosts the voltage so that the inverter can support thecustomer’s load without interruption. If bypass is common with the rectifier input, thebackfeed protection contactor K5 also opens. The opening of contactors K1 and K5prevent system voltages from bleeding backwards through the static switch and rectifiersnubber components and re-entering the input source.While in Battery mode, the UPS sounds an audible horn, illuminates a visual indicator lampon the front panel (System Normal, On Battery), and creates an entry into the alarm eventhistory. As the battery discharges, the converter and inverter constantly make minuteadjustments to maintain a steady output. The UPS remains in this operating mode until theinput power to the rectifier is again within the specified voltage or frequency acceptancewindows.
