Figure 7-4. Path Of Current Through The Ups In Battery Mode - Rt - Powerware 9390 Installation & Operation Manual

Understanding UPS Operation
7.2.4 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.
K1
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 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 feed back 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.
7-8
Static
K5
Switch
Rectifier
Battery
Converter
Closed
Open
Battery
Powerware 9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev C
®
Inverter
CB2
K3
Main Power Flow
Trickle Current
Energized
De-Energized