UNDERSTANDING UPS OPERATIONEaton Power Xpert 9395P-1200 UPS (1200 kVA, 1200 kW) Installation and Operation Manual P-164000500 Rev 4 www.eaton.com/powerquality6-46.2.3 Energy Saver System ModeNOTE VMMS and ESS modes are mutually exclusive. If ESS mode is enabled, VMMS mode is disabled.When the UPS is operating in ESS mode, commercial AC power is supplied directly tothe critical load through the continuous static switch. Power line filtering and spikeprotection for the load are provided by the input and output filter networks, and theUPS actively monitors the critical bus for power disturbances. When in this mode, theinput and output contactors are closed and the link is maintained through the diodebridge.If commercial power voltage or frequency disturbances are detected, the systemforward transfers to Battery mode for minor disturbances and then todouble-conversion mode for more severe disturbances. During a complete poweroutage, the transfer takes place within 2 ms to ensure loads being fed by the systemoutput are not interrupted. All forward transfers transfer to Battery mode beforereturning to double-conversion mode.In High Alert mode the unit transfers from ESS mode to double-conversion mode or ifin double-conversion mode remains in double-conversion mode for a default timeperiod of one hour (customer configurable). At the completion of the time period, theunit defaults back to ESS mode. If the High Alert command is received during thetime period, the timer will be restarted.ESS mode is a normal operating mode, and not an alarm condition. While the UPS isin this mode, the Online light on the front display will illuminate.6.2.4 Variable Module Management SystemNOTE VMMS and ESS modes are mutually exclusive. If VMMS mode is enabled, ESS mode is disabled.In VMMS mode, the UPS operates as a traditional double-conversion UPS. However,the UPS will selectively shift the load to fewer UPMs based on the required load inorder to force the remaining UPMs to carry a higher load. The efficiency rating foreach UPM is highest when loads are greater than 50% of the system rating.Therefore, with multiple UPMs, a UPS can achieve higher efficiencies for lighterloads.When a UPM is placed into VMMS mode, the UPM will stop gating the inverter andrectifier and keep the output contactor closed in order to maintain voltage match andphase lock to the critical bus. In this mode the UPS actively monitors the critical bus,keeping the UPM input contactors closed in order to keep the DC link primed (throughthe rectifier diodes) and also to allow the UPM to immediately return to active modein the event of a disturbance or load step on the critical bus.VMMS limits the maximum power available from a UPM when in VMMS mode. Thedefault setting is 55% of the UPM full power rating. If the limit is exceeded, additionalUPMs take on the increased load. The VMMS redundancy setting sets the number ofredundant UPMs that the customer requires. Both the VMMS UPM load limit andUPM redundancy are customer configurable.
