UNDERSTANDING UPS OPERATIONEATON Power Xpert 9395 UPS (1000–1100 kVA) Installation and Operation Manual 164201764 Rev 3 www.eaton.com/powerquality 6-36.2.2 Online ModeFigure 6‐2 shows the path of electrical power through the UPS system when the UPSis operating in Online mode.During normal UPS operation, power for the system is derived from a utility inputsource through the rectifier input contactor K1. The front panel displays “Online,”indicating the incoming power is within voltage and frequency acceptance windows.Three-phase AC input power is converted to DC using IGBT devices to produce aregulated DC voltage to the inverter. When contactor K2 is closed the battery ischarged directly from the regulated rectifier output through a buck or boost DCconverter, depending on the system voltage and the size of the battery stringattached to the unit.The 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 OutputBypassBreaker(CB4)InputBreaker(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 Mode
