Understanding UPS Operation7-2 EATON Powerware® 9390 UPS (100–160 kVA) Installation and Operation Manual S 164201554 Rev E powerware.comIf utility power is interrupted or falls outside the parameters specified in Chapter 15,“Product Specifications,” the UPS uses a backup battery supply to maintain power to thecritical load for a specified period of time or until the utility power returns. For extendedpower outages, the UPS allows you to either transfer to an alternative power system (suchas a generator) or shut down your critical load in an orderly manner.The emergency bypass consists of a continuous-duty static switch and backfeed protectioncontactor K5. The backfeed protection contactor is located in series with the static switch.For manual transfers to bypass, the static switch is also used. The static switch is armed andready during both types of transfers.The operation of the UPS system is described in greater detail in the following paragraphs.The UPS module may be configured for standalone, single module, Reverse Transfer (RT)operation or multiple module, parallel redundant and/or parallel capacity operation (seeparagraphs 7.2 and 7.3).7.2 Single Module Reverse Transfer (RT)A single module operates independently to support an applied load from the inverter,providing conditioned and uninterruptible AC power to the critical load from the output ofthe module. During an outage, the inverter continues to operate, supporting power to theload from the battery supply. If the unit requires service, applied loads are transferred tothe internal bypass, continuous-duty static switch either automatically or manually. Withthe exception of a battery cabinet, no other cabinets or equipment are required for thesingle module to successfully support its applied loads.7.2.1 Single Module RT ModesThe Powerware 9390 UPS supports a critical load in three different modes of operation.The UPS can automatically use all three modes, as required. The standard operationmodes are: In Normal mode, the critical load is supplied by the inverter, which derives its powerfrom rectified utility AC power. In this mode, the battery charger also provides chargingcurrent for the battery, if needed. In Battery mode, the battery provides DC power, which maintains inverter operation.The battery supports the critical load. In Bypass mode, the critical load is directly supported by utility power.
