UNDERSTANDING UPS OPERATIONEaton Power Xpert 9395P-1200 UPS (1200 kVA, 1200 kW) Installation and Operation Manual P-164000500 Rev 4 www.eaton.com/powerquality 6-3The battery converter derives its input from the regulated DC output of the rectifierand provides either a boosted or bucked regulated DC voltage charge current to thebattery. The battery is always connected to the UPS and ready to support the invertershould the utility input become unavailable.The inverter produces a three-phase AC output to a customer's load without the useof a transformer. The inverter derives regulated DC from the rectifier and uses IGBTdevices and pulse-width modulation (PWM) to produce a regulated and filtered ACoutput. The AC output of the inverter is delivered to the system output through theoutput contactor K3.StaticSwitchRectifier InverterK1 K3BatteryConverterBatteryBatteryBreakerMain Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers ContactorsStaticSwitch K5Rectifier InverterK1 K3Main Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers Contactors K2Bypass 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.Figure 6‐2. Path of Current Through the UPS in Online ModeIf the utility AC power is interrupted or is out of specification, the UPS automaticallyswitches to Battery mode to support the critical load without interruption. When utilitypower returns, the UPS returns to Normal mode.NOTE Bypass mode is not available on a UPS configured as an IOM.If the UPS becomes overloaded or unavailable, the UPS switches to Bypass mode.The UPS automatically returns to Normal mode when the overload condition iscleared and system operation is restored within specified limits.If the UPS suffers an internal failure, it switches automatically to Bypass mode andremains in that mode until the failure is corrected and the UPS is back in service.
