Eaton Power Xpert 9395 Installation And Operation Manual page 133

Understanding UPS Operation
(in case a forward transfer is needed). During this mode, the output contactor is 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 6 . . 2 2 . . 4 4 H H a a r r m m o o n n i i c c R R e e d d u u c c t t i i o o n n S S y y s s t t e e m m ( ( H H R R S S ) )
The Harmonic Reduction system mode of the 9395 UPS allows the UPS to actively reduce the input Total
Demand Distortion (TDD) and increase the input power factor while maintaining high efficiency operation in
ESS mode. The UPS uses one of its UPMs to perform this active harmonic cancellation.
HRS mode uses an extra set of sensors (CTs) on the output bus of the unit. These sensors measure the
harmonics created by loads attached to the UPS output and the system actively reduces these harmonics.
NOTE
HRS is a normal operating mode, not an alarm condition. The Online light appears on the front of the UPS. In
HRS, the inverter is ON, the rectifier is OFF and the output contactor is CLOSED.
If the bypass source falls outside of a predetermined voltage or frequency level, the system forward transfers
to Battery mode and then to Normal mode with the inverter assuming the load. This transfer takes place within
two milliseconds to ensure loads being fed by the system output are not interrupted. All forward transfers go to
Battery mode before returning to Normal mode.
6 6 . . 2 2 . . 5 5 V V a a r r i i a a b b l l e e M M o o d d u u l l e e M M a a n n a a g g e e m m e e n n t t S S y y s s t t e e m m
NOTE
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 80% 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.
112 Eaton Power Xpert 9395 UPS Installation and Operation Manual 164201764—Rev 14
Total Demand Distortion as defined by IEEE 519-1992 is the total root-sum-square
harmonic current distortion, in percent, of the maximum demand load current (the
nameplate rating of a fully rated UPS).
VMMS and ESS modes are mutually exclusive. If VMMS mode is enabled, ESS mode is
disabled.