25-75 kW
User's and Installation Guide
13
2.2.2
Stored Energy and Battery Mode
When running normally in double conversion or ESS mode, the UPS automatically transfers to supply the
load from batteries or other stored energy source if a utility power outage occurs, or if the utility power does
not conform to specified parameters. The UPS status indicated on the display is “On Battery”, and the UPM
status is “Active”. In Battery Mode, the battery provides emergency DC power which is converted to regulated
output power by the inverter. Figure 2-6: Path of current through the UPS in Battery Mode 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 relay K1 opens and the UPS output is powered from
batteries through the inverter. As the inverter operates uninterrupted through the transition, the load remains
supported continuously without disturbance. If the UPS static bypass is supplied from the same source as
the UPS rectifier, the backfeed protection contactor K5 also opens. The opening of K1 and K5 prevent system
voltages from bleeding backwards and re-entering the input source through the static switch or rectifier.
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 a set of audible and visual alarms
indicating that the batteries are having a minimal capacity left and a system shutdown is imminent. Unless
utility power is restored, the output can be supported for maximum 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, K1 and K5 close and the
UPS returns to normal operation. The UPS will also start to recharge batteries to restore the capacity.
Internal relay contacts
Battery breaker
Figure 2-6: Path of current through the UPS in Battery Mode
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