Eaton Power Xpert 9395 Installation And Operation Manual page 134

Understanding UPS Operation
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.
6 6 . . 2 2 . . 6 6 B B y y p p a a s s s s M M o o d d e e
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. Figure 64 shows the path of electrical power through the UPS
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 SCR continuous static switch, and a backfeed protection contactor K5.
The static switch is used instantaneously anytime the inverter is unable to support the applied load. The
continuous static switch is wired in series with the backfeed protection contactor, and together they are wired
in parallel with the rectifier and inverter.
The critical load is not protected from voltage or frequency fluctuations or power outages while the UPS is in
Bypass mode.
The static switch, being an electronically-controlled device, can be turned on immediately to pick up the load
from the inverter while inverter output contactor K3 opens to isolate the inverter. The backfeed protection
contactor is normally closed, ready to support the static switch unless the bypass input source becomes
unavailable.
Eaton Power Xpert 9395 UPS Installation and Operation Manual 164201764—Rev 14 113