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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
voltage required to support the inverter. The input contactor opens and the battery instantaneously supplies energy
to the battery converter. The converter 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 also opens. The
opening of the input and the optional backfeed protection contactors prevent system voltages from bleeding
backwards through the static switch and rectifier snubber components to the utility source.
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, the input and the backfeed
protection contactors 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.
5.3
Single UPS Unit System One line Configurations
The system one line drawings in this section show the simplified internal structure of the UPS, battery supply,
and basic maintenance bypass.
Oneline Drawing
See Figure 5-5
45
UPS Model
See Tab 9-1 for
Model
Eaton 93E MK2 UPS (10-40kVA, 380/400/415V) Installation and Operation
Voltage
Input
Output
380/400/415
380/400/415
System Type
Single Reverse Transfer UPS with External Battery
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