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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 6 . . 2 2 . . 5 5 B B a a t t t t e e r r y y M M o o d d e e
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 48
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. The opening of contactor K1 prevents 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.
If at any time during the battery discharge the input power becomes available again, contactor K1 closes 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.
Figure 48. Path of Current Through the UPS in Battery Mode
Bypass Input
Rectifier
Input
K1
Breakers
Contactors
Closed
Open
Static
Switch
R
c e
f i t
r e i
Battery
Converter
Battery
Breaker
Battery
Eaton 9395XC UPS 1200kW/1200kVA, 1350kW/1350kVA or 1500kW/1500kVA 164001079—Rev 01
Understanding UPS Operation
I
v n
r e
r e t
Main Power Flow
Trickle Current
Energized
De-Energized
Output
87
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