Powerware 9390 UPS 100160 kVA - Manual (Page 63)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9390 UPS (20–80 kVA) Installation and Operation Manual S 164201603 Rev 2 www.powerware.com 7-11
The parallel system can be transferred from Normal mode to Bypass mode manually.
However, the parallel system automatically switches to Bypass mode whenever the
UPMs can no longer supply the critical load. If the parallel system transfers to Bypass
mode from Normal mode due to an output voltage deviation, the parallel system
automatically attempts to return to Normal mode (up to three times within a
10‐minute period). After three transfer attempts or an overload, the system locks the
critical load to the bypass source and requires operator intervention to transfer.
Bypass mode is a normal operating mode, not an alarm condition. However, if the
parallel system is unable to return to Normal mode following an automatic transfer to
Bypass mode, an alarm condition is recorded.
Bypass may also be used when the modules in the system must be shut down to
perform routine maintenance or repairs.
In the Parallel Redundant (N + 1) arrangement, the continuous-duty static switch in
each module operates to support the applied loads on bypass. If both units are in
NORMAL and one unit trips offline, the remaining unit does not go to bypass as long
as it has the capacity to support the load.
In the Parallel Capacity (N + 0) arrangement, if one unit trips offline and goes to
bypass, the remaining units also go to bypass.