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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.
The opening of contactors K1prevent system voltages from bleeding backwards through the
static switch and rectifier snubber components and re-entering the input source.If the finput
power fails to return or is not within the acceptance windows required for normal operatfion
the battery continues discharging until a DC voltage level is reached where the finverter output
can no longer support the connected loads. When this event occurs, the UPS fissues another
set of audible and visual alarms indicating SHUTDOWN IMMINENT. Unless the rectfiffier 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 finstead of
shutting down.
If at any time during the battery discharge the input power becomes available again, contactors
K1 and the rectifier begins to supply DC current to the converter and inverter. At thfis pofint,the
unit returns to normal mode. Depending on the total load and the duration of the battery dfischarge
battery current limit alarms may be seen for a short time due to the current requfired to recharge
the battery.
4.3 UPS system one line configurations
One line drawing
UPS model
Figure 4-5
9395E-200
Voltage
Input
Output
400
400
UPS 200 kVA
User's and Installation Guide
System type
Single module – Reverse transfer
dual-feed
45
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