Eaton Power Xpert 9395P-600/600, Installation And Operation Manual, Page: 146 / 226

128 Eaton ® Power Xpert ® 9395P-600 (300V-600V) Installation and Operation Manual 164000710—Rev 07
If the UPS transfers to Bypass mode from Online mode due to any reason other than operator intervention, the
UPS automatically attempts to transfer back to Online mode (up to three times within a ten minute period). The
fourth transfer locks the critical load to the bypass source and requires operator intervention to transfer.
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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 64 shows the path of electrical power through the UPS system when operating in Battery mode.
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.
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
Online 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.
Understanding UPS Operation