Eaton® 9390 (100–160 kVA) UPS Installation and Operation Manual 164201604—Rev F 42
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Static
Switch
K5
retrevnIreifitceR
K1 K3
Battery
Converter
Battery
CB2
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
During a utility power failure, the rectifier no longer has an AC utility source from which to supply the DC output
current required to support the inverter. The input contactor K1 opens and the battery instantaneously supplies
energy to the battery converter. The converter either bucks or boosts the voltage so that the inverter can
support the customer's load without interruption. If bypass is common with the rectifier input, the backfeed
protection contactor K5 also opens. The opening of contactors K1 and K5 prevent system voltages from
bleeding backwards through the static switch and rectifier snubber components and re-entering the input
source.
While in Battery mode, the UPS sounds an audible horn, illuminates a visual indicator lamp on the front panel
(System Normal, On Battery), and creates an entry into the alarm event history. As the battery discharges, the
converter and inverter constantly make minute adjustments to maintain a steady output. The UPS remains in
this operating mode until the input power to the rectifier is again within the specified voltage or frequency
acceptance windows.
If the input power fails to return or is not within the acceptance windows required for normal operation, the
battery continues discharging until a DC voltage level is reached where the inverter output can no longer
support the connected loads. When this event occurs, the UPS issues another set of audible and visual alarms
indicating SHUTDOWN IMMINENT. Unless the rectifier has a valid AC input soon, the output can be supported
for only two minutes before the output of the system shuts down. If the bypass source is available, the UPS
transfers to bypass instead of shutting down.
If at any time during the battery discharge the input power becomes available again, contactors K1 and K5 close
and the rectifier begins to supply DC current to the converter and inverter. At this point, the unit returns to
Normal mode. Depending on the total load and the duration of the battery discharge, battery current limit
alarms may be seen for a short time due to the current required to recharge the battery.
The system's total operating time on battery depends on many factors. Some factors that affect battery
support times are battery type and capacity, number of parallel strings, environmental temperatures, age of the
Understanding UPS Operation
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