UNDERSTANDING UPS OPERATION
Eaton
Power Xpert 9395P UPS (300 kVA, 300 kW) Installation and Operation Manual
S
P-164000563 Rev 1
www.eaton.com/powerquality
6-24
Main Power Flow
UPS 1
UPS 2
UPS 3
UPS 4
Output to
Critical Load
Battery
UPS Input
Tie Cabinet
UPS 1 Output
Bypass Input
UPS 2 Output
UPS 3 Output
UPS 4 Output
Battery
Battery
Battery
Closed
Open
Breakers
Figure 6‐17. Path of Current through the UPSs in Bypass Mode – Distributed Bypass
The distributed bypass system can be transferred from Normal mode to Bypass mode
manually. However, the distributed bypass system automatically switches to Bypass
mode whenever the UPSs can no longer supply the critical load. If the distributed
bypass system transfers to Bypass mode from Normal mode due to an output voltage
deviation, the distributed bypass 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
distributed bypass 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 UPSs or UPMs in the system must be shut down
to perform routine maintenance or repairs.
In the Parallel Redundant (N+1) arrangement, the bypass circuitry in each UPS
operates to support the applied loads on bypass. If the UPSs are online and one UPS
trips offline, the remaining UPSs do not go to bypass as long as they have the
capacity to support the load.
In the Parallel Capacity (N+0) arrangement, if one UPS trips offline and goes to
bypass, the remaining UPSs also go to bypass.
