Powerware 9390 UPS 100160 kVA - Manual (Page 58)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9390 UPS (20–80 kVA) Installation and Operation Manual S 164201603 Rev 2 www.powerware.com 7-6
7.1.4 Battery Mode – RT
The UPS automatically transfers to Battery mode 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 7‐4 shows the path of electrical power through the UPS system when
operating in Battery mode.
Static
Switch
K5
Rectifier Inverter
K1 K3
Battery
Converter
Battery
CB2
Main Power Flow
Trickle Current
Energized
De-Energized
Closed
Open
Breakers Contactors
Figure 7‐4. Path of Current Through the UPS in Battery Mode – RT
During a utility power failure, the rectifier no longer has an AC utility source from
which to supply the DC output current required to support the inverter. The input
contactor K1 opens and the battery instantaneously supplies energy to the battery
converter. The converter either bucks or boosts the voltage so that the inverter can
support the customer's load without interruption. If bypass is common with the
rectifier input, the backfeed protection contactor K5 also opens. The opening of
contactors K1 and K5 prevent system voltages from bleeding backwards through the
static switch and rectifier snubber components and re-entering the input source.
While in Battery mode, the UPS sounds an audible horn, illuminates a visual indicator
lamp on the front panel (System Normal, On Battery), and creates an entry into the
alarm event history. As the battery discharges, the converter and inverter constantly
make minute adjustments to maintain a steady output. The UPS remains 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 connected loads. When this
event occurs, the UPS issues another set of audible and visual alarms indicating
SHUTDOWN IMMINENT. Unless the rectifier has a valid AC input soon, the output
can be supported for only two minutes before the output of the system shuts down.
If the bypass source is available, the UPS transfers to bypass instead of shutting
down.