Eaton Power Xpert 9395P-1100/1100 Installation And Operation Manual page 134

Understanding UPS Operation
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 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.
VMMS's UPM automatic scheduling rotates the idle UPMs every month with the ABM cycle. This allows the
UPMs to have equal load-share time and also conducts a periodic UPM readiness test. The automatic ABM
scheduler selects the next UPM in turn after each charge-to-float transition. If ABM is disabled, the scheduler
selects the next UPM after conducting the automatic battery test. If ABM and automatic battery tests are
disabled, the scheduler selects the next UPM at the beginning of each month.
In High Alert mode, the UPS defaults to double-conversion Online mode and all UPMs go active for one hour
(customer configurable). At the completion of the hour, the UPS defaults back to VMMS mode. If the High Alert
command is received during the one hour, the one hour timer will be restarted.
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NOTE
The UPS automatically switches to Bypass mode if it detects an overload, load fault, or internal failure. The UPS
can also be transfered from Online mode to Bypass mode manually. The bypass source supplies the
commercial AC power to the load directly.
system when operating in Bypass mode.
In Bypass mode, the output of the system is provided with three-phase AC power directly from the system
input. While in this mode, the output of the system is not protected 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
active power conditioning or battery support is available to the output of the system in the Bypass mode of
operation.
The internal bypass is comprised of a solid-state, silicon-controlled rectifier (SCR) static switch (SSW) and a
backfeed protection contactor K5. The static switch is rated as a continuous-duty device that is used anytime
116 Eaton ®
VMMS and ESS modes are mutually exclusive. If VMMS mode is enabled, ESS mode is
disabled.
Bypass mode is not available on a UPS configured as an IOM.
Power Xpert ® 9395P-1200 Installation and Operation Manual 164000500—Rev 11
Figure 64 shows the path of electrical power through the UPS