UNDERSTANDING UPS OPERATIONEATON Eaton 9395 550/275 UPS (225–550 kVA) Installation and Operation Manual 164201716 Rev 2 www.eaton.com/powerquality6-26.2 Single UPSA single UPS operates independently to support an applied load from the inverter,providing conditioned and uninterruptible AC power to the critical load from the outputof the module. During an outage, the inverter continues to operate, supporting powerto the load from the battery supply. If the unit requires service, applied loads aretransferred to the internal bypass, continuous-duty static switch either automaticallyor manually. With the exception of a battery cabinet, no other cabinets or equipmentare required for the single UPS to successfully support its applied loads.6.2.1 ModesThe Eaton9395 UPS supports a critical load in five different modes of operation:NOTE The Variable Module Management System and Energy Saver System modes are mutually exclusive. In Online mode, the critical load is supplied by the inverter, which derives its powerfrom rectified utility AC power. In this mode, the battery charger also providescharging current for the battery, if needed. In Energy Saver System (ESS) mode, commercial AC power is supplied directly tothe critical load through the continuous static switch and transfers automatically toOnline mode if an abnormal condition is detected. In Variable Module Management System (VMMS) mode, the UPS operates as atraditional double-conversion UPS, but selectively shifts the load to fewer UPMs toincrease the efficiency of the UPS. In Bypass mode, the critical load is directly supported by utility power. In Battery mode, the battery provides DC power, which maintains inverteroperation. The battery supports the critical load.The following paragraphs describe the differences in the UPS operating modes, usingblock diagrams to show the power flow during each mode of operation.6.2.2 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.
