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Understanding U PS Operation
3-4
EATON Powerware
®
9315 UPS (200–300 kVA) Operatio n Manual S 164201036 Rev F powerware.com
3.3 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
provides emergency DC power that the inverter converts to AC power. When the UPS
switches to Battery mode, the alarm indications depend on the c ause and condition of the
battery charge. The length of time the system can operate in Battery mode depends on
load configuration and the battery charge.
Figure 3-3 shows the path of electrical power through the UPS when operating in Battery
mode.
Bypass
Input
Rectifier
Input
Output
Path of electrical power
Battery
Rectifier Inverter
Bypass
K4
Transformer
K3
(Closed)
CB1
Figure 3-3. 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 two minutes, depending on load configuration and the battery charge.
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.