Understanding UPS Operation7-10 EATON Powerware® 9390 UPS (100–160 kVA) Installation and Operation Manual S 164201554 Rev E powerware.comUp to four units can be paralleled for redundancy or capacity without any additionalcabinets.The system is paralleled for redundancy (1+1) in a system where two UPMs are paralleledtogether and the load is less than the supporting capability of one of the UPMs. The systemis paralleled for capacity (2+0) if both UPMs in a system are required to support the load.A parallel capacity system can also be redundant (2+1), as long as there is always one ormore UPMs online than required to support the load.7.3.1 Multiple Module Parallel System ModesSimilar to the single module system, the Powerware 9390 UPS parallel system supports acritical load in three different modes of operation. The standard operation modes are: In Normal mode, the paralleled UPMs supply the critical load with clean, filtered power.Each UPM battery charger also provides charging current for the battery if needed. In Battery mode, the battery provides DC power, which maintains UPM operation. TheUPM batteries support the critical load. In Bypass mode, the critical load is directly supported by utility power through thecontinuous-duty static bypass switch in each UPM.The UPMs continually monitor themselves and the incoming utility power, andautomatically switch between these modes as required, without operator intervention,except when manually switching to Bypass mode. The sophisticated detection andswitching logic inside the UPMs ensures that operating mode changes are automatic andtransparent to the critical load, while internal monitoring systems indicate the currentmode of operation. The UPMs switch operating modes in response to these system events: A command is an intervention that is externally initiated by an operator or by some siteaction. A command causes the UPMs to switch operating modes; it usually does notrequire any further action. A notice is a minor system event that may or may not require attention. An alarm is a system event that requires immediate intervention.System events, alarm horns, and indicator lights are described in Chapter 12, “Respondingto System Events.”To assist in developing an understanding of the parallel system modes of operation, reviewand understand thoroughly the single module modes of operation.The following paragraphs describe the differences in the three parallel system operatingmodes, using block diagrams to show the power flow during each mode of operation.
