Eaton Power Xpert 9395 550/275, Installation And Operation Manual

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Understanding UPS Operation
6-6 Power Xpert
TM
9395 550/275 UPS (225–550 kVA) Installation and Operation Manual 164201716—Rev 8 www.eaton.com/powerquality
6.2.7 Battery Mode
The UPS automatically transfers to Battery mode if a utility power outage occurs, or if the utility power does
not conform to specified parameters. In Battery mode, the battery provides emergency DC power that the
inverter converts to AC power.
Figure 6-4 shows the path of electrical power through the UPS system when operating in Battery mode.
Figure 6-4. Path of Current Through the UPS in Battery Mode
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.
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
Online 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.
Static
Switch
K5
r e t r e v n I r e i f i t c e R
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
K2
Input
Breaker
(CB1
Bypass Input
Rectifier
Input
Output