Powerware 5075 kVA - Manual (Page 51)

43 Powerware BPIII Harsh Environment UPS 50--75 kVA Installation and Operatio n
164201261 Rev. F 111503
Battery Mode
The UPS transfers to Battery mode automatically if a utility power outage occurs, or
if the utility power does not conform to specified parameters. In Battery mode, the
battery, through the DC to DC voltage converter, provides emergency DC power
that the inverter converts to AC power. When the UPS switches to Battery mode,
the alarm indications depend on the cause and condition of the battery charge.
The length of time the system can operate in Battery mode depends on loading
and the battery supply capacity.
Figure 20 shows the path of electrical power through the UPS when operating in
Battery mode.
Bypass
Rectifier
K4
Input
Input
K3 CB1
(closed)
BATTERY
Path of electrical power
RECTIFIER INVERTER
Output
TRANSFORMER
BYPASS
DC/DC
CONVERTER
CB2
(closed)
(MBP)
(open)
Input
Isolation
Transformer
(BIB)
(closed)
(MIS)
(closed)
OUTPUT
Figure 20. Path of Current Through the UPS in Battery Mode
When the discharging battery voltage reaches the lower limit of UPS operation
capability, the critical load transfers to Bypass mode if it is available. If Bypass input
is not available, a “Shutdown Imminent” warning occurs. The warning time before
critical load loss occurs is approximately 2 minutes, depending on battery capacity
and the amount of loading.
If incoming power returns to within specified parameters, the UPS automatically
returns to Normal mode and alarm indications clear. However, the process of returning
to Normal mode is not instantaneous. The rectifier gradually draws increasing power
from the incoming utility until Normal mode is achieved.