Eaton 91PS UPS 8-40 kW User And Installation Manual page 24

Eaton 91PS/93PS UPS 8–40 kW
Figure 6. Path of current through the UPS in the battery mode
A Static
switch
B Rectifier
C Inverter
D Battery con-
verter
E Battery
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 battery continues discharging until a DC voltage level
is reached where the inverter output can no longer support the connected loads.
The UPS issues a Low Battery alarm to indicate that the battery voltage level is
running low. The UPS continues to discharge the batteries until the battery
voltage reaches the threshold level of the Low Battery alarm. If the bypass is
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Eaton Corporation plc 2018. All rights reserved.
1 Bypass in-
put
2 Rectifier in-
put
3 Output
4 Battery
breaker
Closed
Revision: 005
User's and installation guide
Main power flow
Energized
De-energized
Trickle current
Open
Document ID: P-164000493 24 (117)