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Understanding UPS Operation
If the input power fails to return or is not within the acceptance windows required for
normal operation, the battery will continue discharging until a DC voltage level is reached
where the inverter output can no longer support the connected loads. When this occurs,
the unit will issue another set of audible and visual alarms indicating SHUTDOWN
IMMINENT. Unless the rectifier has a valid input soon, the output will only be supported
for 2 minutes before the output of the system shuts down. If the bypass source is
available, the system will transfer to Bypass instead of shuting down.
If at any time during the battery discharge the input power becomes available again,
contactors K1 and K5 are closed and the rectifier will begin to supply DC current to the
converter and inverter. At this point, the unit returns to normal operation. Depending on
the amount of load on the system 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.
The systems total operating time on battery will depend on many factors. Some factors
that affect battery support times are battery type and capacity, number of parallel strings,
environmental temperatures, age of the battery, and fluctuations in load demand during
the discharge. The greater the load, the less support time the battery will have. Decrease
the load, and the battery support time will generally increase.
6-8
Powerware
9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev A
®
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