PowerWalker VFI 20000-40000TAP 3/3 BI, User Manual

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5-5
5.2.5 Battery Mode
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 5-4 shows the path of electrical power through the UPS system when operating in Battery mode.
Figure 5-4. Path of Current Through the UPS in standard Battery Mode
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.
Bypass Input
Rectifier
Input
Switch
Input
Relay
Output
Relay
Output
Relay
Closed
Main Power Flow
Trickle Current
Energised
De-Energised
Open
Battery
Converter
Inverter
Battery
Relay
Battery
Rectifier
Static
Switch
Bypass Switch (Optional Dual Input)
Input Switch