UNDERSTANDING UPS OPERATION
Eaton
Power Xpert 9395P UPS (300 kVA, 300 kW) Installation and Operation Manual
S
P-164000563 Rev 1
www.eaton.com/powerquality
6-25
6.4.4
Battery Mode – Distributed Bypass
The UPSs transfer 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.
Figure 6‐18 shows the path of electrical power through the distributed bypass system
when operating in Battery mode.
While in Battery mode, the UPSs sound an audible horn, illuminate a visual indicator
lamp on the front panel (Online and On Battery), and create an entry into the alarm
event history. As the battery discharges, the boost converter and inverter constantly
make minute adjustments maintaining a steady output. The UPSs remain in this
operating mode until the input power to the rectifier is again within the specified
voltage or frequency acceptance windows.
If the input power fails to return or is not within the acceptance windows required for
normal operation, the battery continues discharging until a DC voltage level is reached
where the inverter output can no longer support the shared loads. When this event
occurs, each UPS issues another set of audible and visual alarms that indicate a
two-minute SHUTDOWN IMMINENT warning. Unless the system has a valid AC
input soon, redundant UPMs begin shutting down until there are no longer enough
UPMs online to support the connected load. When this event occurs, the system
shuts down. If the bypass source is available, the system transfers to bypass instead
of shutting down.
Main Power Flow
UPS 1
UPS 2
UPS 3
UPS 4
Output to
Critical Load
Battery
UPS Input
Tie Cabinet
UPS 1 Output
Bypass Input
UPS 2 Output
UPS 3 Output
UPS 4 Output
Battery
Battery
Battery
Closed
Open
Breakers
Figure 6‐18. Path of Current through the UPSs in Battery Mode – Distributed Bypass
