Understanding UPS OperationPower Xpert TM 9395 UPS (450–825 kVA) Installation and Operation Manual 164201725—Rev 10 www.eaton.com/powerquality 6-76.2.7 Battery ModeThe UPS automatically transfers to Battery mode if a utility power outage occurs, or if the utility power doesnot conform to specified parameters. In Battery mode, the battery provides emergency DC power that theinverter converts to AC power.Figure 6-4 shows the path of electrical power through the UPS system when operating in Battery mode.During a utility power failure, the rectifier no longer has an AC utility source from which to supply the DC outputvoltage required to support the inverter. The input boosts the voltage so that the inverter can support thecustomer's load without interruption. If bypass is common with the rectifier input, the backfeed protectioncontactor K5 also opens. The opening of contactors K1 and K5 prevent system voltages from bleedingbackwards through the static switch and rectifier snubber components to the utility source.Figure 6-4. Path of Current Through the UPS in Battery ModeIf the input power fails to return or is not within the acceptance windows required for normal operation, thebattery continues discharging until a DC voltage level is reached where the inverter output can no longersupport the connected loads. When this event occurs, the UPS issues another set of audible and visual alarmsindicating SHUTDOWN IMMINENT. Unless the rectifier has a valid AC input soon, the output can be supportedfor only two minutes before the output of the system shuts down. If the bypass source is available, the UPStransfers to bypass instead of shutting down.StaticSwitch K5retrevnIreifitceRK1 K3BatteryConverterBatteryBatteryBreakerMain Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers ContactorsK2BypassBreaker(CB4)Bypass InputRectifierInput OutputInputBreaker(CB1NOTE On a UPS configured as an IOM, the bypass input, static switch, bypass breaker (CB4), and K5 are not present.NOTE On a UPS configured with a Continuous Static Switch (CSS), bypass breaker (CB4) is not present.
