The UPS switches automatically back to the ESS mode after the input voltages and frequency have been
within the acceptable limits for an appropriate time.
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When running normally in the double conversion, VMMS, or ESS mode, the UPS automatically transfers
to supply the load from batteries or some other stored energy source if a utility power outage occurs, or if
the utility power does not conform to the specified parameters. The UPS status indicated on the display is
On Battery, and the UPM status is Active. In the stored energy mode, the DC source provides
emergency DC power, which is converted to regulated output power by the inverter.
Figure
7: Path of current through the UPS in the battery mode shows the path of electrical power through
the UPS system when operating in the battery mode.
Figure 7. Path of current through the UPS in the battery mode
A Static switch 1 Bypass input Main power flow
B Rectifier 2 Rectifier input
Energized
C Inverter 3 Output
De-energized
D DC/DC converter 4 Battery breaker
Trickle current
E Battery
Closed Open
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 relay K1 opens and the UPS output is powered
from the batteries through the inverter. As the inverter operates uninterrupted through the transition, the
load remains supported continuously without disturbance. If the UPS static bypass is supplied from the
same source as the UPS rectifier, the backfeed protection contactor K5 also opens. The opening of K1
and K5 prevent system voltages from bleeding backwards and re-entering the input source through the
static switch or rectifier.
If the input power fails to return or is not within the acceptance windows required for normal operation, the
DC/DC converter continues discharging the stored energy source until the end-of-discharge battery
EATON 93PM G2 UPS USER’S AND INSTALLATION GUIDE P-164000956
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February 2021 www.eaton.eu 2233
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