UNDERSTANDING UPS OPERATIONEaton Power Xpert 9395P-1200 UPS (1200 kVA, 1200 kW) Installation and Operation Manual P-164000500 Rev 4 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 ModeNOTE Bypass mode is not available on a UPS configured as an IOM.The UPS automatically switches to Bypass mode if it detects an overload, load fault,or internal failure. The UPS can also be transferred from Normal mode to Bypassmode manually. 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.In 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.The internal bypass is comprised of a SCR continuous static switch, and a backfeedprotection contactor K5. The static switch is used instantaneously anytime theinverter is unable to support the applied load. The continuous static switch is wired inseries with the backfeed protection contactor, and together they are wired in parallelwith the rectifier and inverter.C A U T I O NThe critical load is not protected from voltage or frequency fluctuations or power outages while the UPS is inBypass mode.MISE EN GARDE!Les charges critiques ne sont pas protégées des fluctuations de tension ou de fréquence ni des pannes decourant lorsque l’onduleur est en mode Contournement.The static switch, being an electronically-controlled device, can be turned onimmediately to pick up the load from the inverter while inverter output contactor K3opens to isolate the inverter. The backfeed protection contactor is normally closed,ready to support the static switch unless the bypass input source becomesunavailable.
