16
30-200 kW
P-164000249
User's and Installation Guide
Revision 2
Internal relay contacts
Battery breaker
Figure 2-6: Path of current through the UPS 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.
2.2.3 Bypass mode
The UPS automatically switches to bypass mode if it detects an overload, load fault, or internal failure.
The bypass source supplies the commercial AC power to the load directly. The UPS can also be
commanded to transfer to bypass manually through the display. The UPS status indicated on the
display is “On Bypass”.
Figure 2-7: Path of current through the UPS in bypass mode
on page 17
shows the path of electrical power through the UPS system when operating in Bypass mode.
