UNDERSTANDING UPS OPERATION
Eaton
Power Xpert 9395P-600 (380V-600V) UPS Installation and Operation Manual
S
P-164000710 Rev 1
www.eaton.com/powerquality
6-4
6.2.3
Energy Saver System Mode
NOTE
Variable Module Management System (VMMS) and Energy Saver System (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 to
the critical load through the continuous static switch. Power line filtering and spike
protection for the load are provided by the input and output filter networks, and the
UPS actively monitors the critical bus for power disturbances. When in this mode, the
input and output contactors are closed and the link is maintained through the diode
bridge.
If commercial power voltage or frequency disturbances are detected, the system
forward transfers to Battery mode for minor disturbances and then to
double-conversion mode for more severe disturbances. During a complete power
outage, the transfer takes place within 2 ms to ensure loads being fed by the system
output are not interrupted. All forward transfers transfer to Battery mode before
returning to double-conversion mode.
In High Alert mode the unit transfers from ESS mode to double-conversion mode or if
in double-conversion mode remains in double-conversion mode for a default time
period of one hour (customer configurable). At the completion of the time period, the
unit defaults back to ESS mode. If the High Alert command is received during the
time period, the timer will be restarted.
ESS mode is a normal operating mode, and not an alarm condition. While the UPS is
in this mode, the Online light on the front display will illuminate.
6.2.4
Variable Module Management System
NOTE
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 in
order to force the remaining UPMs to carry a higher load. The efficiency rating for
each UPM is highest when loads are greater than 50% of the system rating.
Therefore, with multiple UPMs, a UPS can achieve higher efficiencies for lighter
loads.
When a UPM is placed into VMMS mode, the UPM will stop gating the inverter and
rectifier and keep the output contactor closed in order to maintain voltage match and
phase 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 (through
the rectifier diodes) and also to allow the UPM to immediately return to active mode
in 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. The
default setting is 55% of the UPM full power rating. If the limit is exceeded, additional
UPMs take on the increased load. The VMMS redundancy setting sets the number of
redundant UPMs that the customer requires. Both the VMMS UPM load limit and
UPM redundancy are customer configurable.
