Figure 51. Path Of Current Through The Ups In Battery Mode - Eaton Power Xpert 9395 550/275 Installation And Operation Manual

Understanding UPS Operation
contactor is normally always closed, ready to support the static switch unless the bypass input source
becomes unavailable.
If the UPS transfers to Bypass mode from Online mode due to any reason other than operator intervention, the
UPS automatically attempts to transfer back to Online 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 . . 7 7 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 51 shows the path of electrical power through the UPS system when operating in Battery mode.

Figure 51. Path of Current Through the UPS in Battery Mode

Bypass Input
Input
Breaker
Rectifier (CB1
Input
K1
Breakers Contactors
NOTE On a UPS configured as an IOM, the bypass input, static switch, and K5 are not present.
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
96 Eaton Power Xpert 9395 UPS Installation and Operation Manual 164201716—Rev 14
Static
Switch
R c e f i t r e i
Battery
Converter
Closed
Open
Battery
K5
I v n r e r e t
K2
Battery
Breaker
Output
K3
Main Power Flow
Trickle Current
Energized
De-Energized