UNDERSTANDING UPS OPERATION
EATON Powerware
®
9315 UPS (500–750 kVA) Installationand Operation Manual S 164201691 Rev 1 www.powerware.com
7-5
7.1.3 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 cause and
condition of the battery charge. The length of time the system can operate in Battery
mode depends on load configuration and battery charge.
Figure 7-4 shows the path of electrical power through the UPS system when the UPS
is operating in Battery mode.
FBP
Input
Transformer
Path ofElectrical Power
InverterRectifier
DC
Link
CB2
(closed)
Output
Transformer
(closed)
CB3
(closed)
CB1
Rectifier
Input
Bypass
Input
(open)
Output
Static Switch
(open)
CB4
Bypass
Battery
Figure 7-4. Path of Current Through the UPS in Battery Mode
When thedischarging batteryvoltage reachesthe lower limitof UPSoperation capability,
thecritical loadtransfers toBypass modeif itis available.If Bypassinput isnot available,a
Shutdown Imminent warning occurs. The warning time before critical load loss occurs is
approximately two minutes, depending on load configuration and battery charge.
If incoming power returns to within specified parameters, the UPS automatically returns
toNormal modeand alarm indicationsclear.However, theprocess ofreturningt o Normal
mode is not instantaneous. The rectifier gradually draws increasing power from the
incoming utility until Normal mode is achieved.
