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3.3.4 Input Power Failure—Load on Battery
If the utility AC power source fails or is outside the acceptable range, the battery plant becomes the
power source for the UPS module inverters. The UPS system continues to supply power to the critical
load and also to the UPS controls.
You can use the Battery Time screen at the UPS modules to monitor the present battery voltage com-
pared to the shutdown value. The length of time the battery can sustain the load depends on the size
of the load and the size and condition of the battery plant. The battery plant is typically large enough
to supply a 100% rated load for 10-15 minutes.
Alarm messages that indicate battery status are Battery Discharge, Low Battery and Battery Shut-
down. The voltage limits for these alarms are displayed on the UPS module Alarm Limit Settings
screen. These limits were selected for your installation by Liebert Global Services during initial start-
up.
The battery block in the UPS module Monitor/Mimic Display indicates Charge or Discharge and the
current in Amperes. Maximum battery discharge current ranges from 326 amps (for 150kVA) to 1619
amps (for 750kVA). Refer to the separate Installation Manual or drawings for specific data on your
system.
Figure 45 Input power fail—load on battery
OUTPUT
CB
Controls
Battery
Bypass CB
INPUT
CB
Static
Bypass
Switch
RIB
BFB
Critical
Load
AC Output
MBD
Static
Switch
Disconnects
THREE BREAKER MAINTENANCE BYPASS SWITCHBOARD
CONTROL POWER
UPS MODULE
MAIN INPUT
SWITCHGEAR
Rectifier/
Charger
Inverter
MBB
MIB
BIB