UNDERSTANDING UPS OPERATIONPower Xpert 9395 UPS (300 kVA) Installation and Operation Manual 164201728 Rev 2 www.eaton.com/powerquality 6-5VMMS's UPM automatic scheduling rotates the idle UPMs every month with theABM cycle. This allows the UPMs to have equal load-share time and also conducts aperiodic UPM readiness test. The automatic ABM scheduler selects the next UPM inturn after each charge-to-float transition. If ABM is disabled, the scheduler selects thenext UPM after conducting the automatic battery test. If ABM and automatic batterytests are disabled, the scheduler selects the next UPM at the beginning of eachmonth.In High Alert mode, the UPS defaults to double-conversion Online mode and all UPMsgo active for one hour (customer configurable). At the completion of the hour, theUPS defaults back to VMMS mode. If the High Alert command is received during theone hour, the one hour timer will be restarted.6.2.5 Bypass ModeThe UPS automatically switches to Bypass mode if it detects an overload, load fault,or internal failure. The bypass source supplies the commercial AC power to the loaddirectly. Figure 6‐3 shows the path of electrical power through the UPS system whenoperating in Bypass mode.C A U T I O NThe critical load is not protected while the UPS is in Bypass mode.StaticSwitch K5Rectifier InverterK1 K3BatteryConverterBatteryBatteryBreakerMain Power FlowTrickle CurrentEnergizedDe-EnergizedClosedOpenBreakers ContactorsK2Bypass InputRectifier Input OutputFigure 6‐3. Path of Current Through the UPS in Bypass ModeIn Bypass mode, the output of the system is provided with three-phase AC powerdirectly from the system input. While in this mode, the output of the system is notprotected from voltage or frequency fluctuations or power outages from the source.Some power line filtering and spike protection is provided to the load but no activepower conditioning or battery support is available to the output of the system in theBypass mode of operation.
