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Understanding UPS Operation
7-12
EATON Powerware
®
9390 UPS (100–160 kVA) Installation and Operation Manual S 164201604 Rev B powerware.com
7.3.3 Bypass Mode – Parallel
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 power filtering, conditioning, or
battery support is available to the output of the system in the Bypass mode of operation.
The parallel system automatically switches to Bypass mode if it detects a UPM overload,
UPMs unavailable, load fault, or internal failure.
Figure 7-6 shows the path of electrical power through the parallel system when operating
in Bypass mode.
Main Power Flow
UPM 1
UPM 2
UPM 3
UPM 4
Output to
Critical
Load
Battery
UPM Input
Module Tie Cabinet
UPM 1 Output
Bypass Input
UPM 2 Output
UPM 3 Output
UPM 4 Output
Battery
Battery
Battery
Closed
Open
Breakers
Figure 7-6. Path of Current through the UPMs in Bypass Mode – Parallel
In a parallel redundant or capacity type system, each module operates similar to a single
module, but in parallel with each other. The bypass source for the load is derived from the
bypass input of one, two, three, or four modules, depending on the system configuration
through the internal continuous-duty static switches. If a module is taken offline, the other
modulesremainonlinetosupporttheload.Ifmoremodulesthancansupporttheload
must be taken offline, the load must be transferred to maintenance bypass or shut down.