Understanding UPS Operation
6-6
Eaton
®
Power Xpert
®
9395P-900 UPS Installation and Operation Manual
P-164000501—Rev 09
www.eaton.com/powerquality
Figure 6-3. Path of Current Through the UPS in Bypass Mode
If the UPS transfers to Bypass mode from Normal mode due to any reason other than operator intervention,
the UPS automatically attempts to transfer back to Normal mode (up to three times within a ten minute period).
The fourth transfer locks the critical load to the bypass source and requires operator intervention to transfer.
6.2.6
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.
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 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 battery continues
discharging until a DC voltage level is reached where the inverter output can no longer support the shared
loads. If the bypass source is available, the UPS transfers to bypass instead of shutting down.
Static
Switch
K5
r
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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
Bypass Input
Rectifier
Input
Output
Input
Breaker
(CB1
NOTE
On a UPS configured as an IOM, the bypass input, static switch, bypass breaker (CB4), and K5 are not present.
NOTE
On a UPS configured with a Continuous Static Switch (CSS), bypass breaker (CB4) is not present.
Summary of Contents for Power Xpert 9395P-900 Series
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