Eaton® 9390 (100–160 kVA) UPS Installation and Operation Manual 164201604—Rev F 44
• A command is an intervention that is externally initiated by an operator or by some site action. A command
causes the UPMs to switch operating modes; it usually does not require any further action.
• A notice is a minor system event that may or may not require attention.
• An alarm is a system event that requires immediate intervention.
System events, alarm horns, and indicator lights are described in Chapter 11 Responding to System Events.
To assist in developing an understanding of the parallel system modes of operation, review and understand
thoroughly the single module modes of operation.
The following sections describe the differences in the three parallel system operating modes, using block
diagrams to show the power flow during each mode of operation.
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In Normal mode, utility AC power is supplied to the UPMs. Each UPM then conditions the incoming AC power
and provides clean, regulated AC power to either a module tie cabinet or distribution panel for parallel systems
up to four modules. The applied load is equally shared among the available UPMs in the system.
Figure 14 shows the path of electrical power through the parallel system when operating in Normal mode.
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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
Understanding UPS Operation
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