Emerson 250-400kVA - Manual (Page 27)

Operation
21
2.3.3 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 continues to supply power to the critical load
and also to the UPS controls.
Use the Battery Time screen at the UPS modules to monitor the present battery voltage compared to
the shutdown value. The time the battery can sustain the load depends on the size of the load and the
size and condition of the battery plant.
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 Services during initial startup. The
battery block in the UPS module Monitor/Mimic Display indicates Charge or Discharge and the cur-
rent in amperes.
Figure 26 Input power fail, load on battery
Bypass
Input
Battery
System
DC Bus
Module
Output
BFB
CB2 CB1
MBD