Eaton Power Xpert 9395 UPS, Installation And Operation Manual

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Understanding UPS Operation
Power Xpert
TM
9395 UPS (450–825 kVA) Installation and Operation Manual 164201725—Rev 10 www.eaton.com/powerquality 6-5
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.
6.2.6 Bypass Mode
The UPS automatically switches to Bypass mode if it detects an overload, load fault, or internal failure. The UPS
can also be transferred from Online mode to Bypass mode manually. The bypass source supplies the
commercial AC power to the load directly. Figure 6-3 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.
CAUTION
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.
NOTE Bypass mode is not available on a UPS configured as an IOM.