Powerware 9395 UPS 10001100 kVA - Manuel (Page 109)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9395 UPS (1000–1100 kVA) Installation and Operation Manual S 164201764 Rev 1 www.powerware.com 6−5
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.
Static
Switch
K5
Rectifier Inverter
K1 K3
Battery
Converter
Battery
Battery
Breaker
Main Power Flow
Trickle Current
Energized
De−Energized
Closed
Open
Breakers Contactors
K2
Bypass
Breaker
(CB4)
Bypass Input
Rectifier
Input
Output
Input
Breaker
(CB1
Figure 6-4. Path of Current Through the UPS in Battery Mode
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.
If at any time during the battery discharge the input power becomes available again,
contactors K1 and K5 close and the rectifier begins to supply DC current to the
converter and inverter. At this point, the unit returns to Normal mode. Depending on
the total load and the duration of the battery discharge, battery current limit alarms
may be seen for a short time due to the current required to recharge the battery.