Eaton Power Xpert 9395 550/275, Installation And Operation Manual

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Understanding UPS Operation
Power Xpert
TM
9395 550/275 UPS (225–550 kVA) Installation and Operation Manual 164201716—Rev 8 www.eaton.com/powerquality 6-15
Figure 6-10. Path of Current through the UPSs in Online Mode – Distributed Bypass
6.4.3 Bypass Mode –

Distributed Bypass
In Bypass mode, the output of the system is provided with three-phase AC power directly from the bypass
input. While in this mode, the output of the system is not protected from fluctuations, spikes, or power outages
from the source. No battery support is available to the output of the system in the Bypass mode of operation.
The distributed bypass system automatically switches to Bypass mode if it detects a UPS system overload or
load fault.
If one UPS becomes unavailable, the distributed bypass system dynamically updates the redundancy
calculation to determine if the remaining UPSs can support the load. If the load can be supported, the system
does not switch to bypass.
Figure 6-11 shows the path of electrical power through the parallel system when operating in Bypass mode.
In a distributed bypass system, each UPS operates similar to a single UPS, but in parallel with each other. The
bypass source for the load is derived from the bypass input of one, two, three, or four UPSs, depending on the
system configuration, through the internal static switches. If a module is taken offline, the other modules
remain online to support the load. If more modules than can support the load must be taken offline, the load
must be transferred to maintenance bypass or shut down.
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