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Understanding UPS Operation
Up to four units can be paralleled for redundancy or capacity without any additional
cabinets.
The system is paralleled for redundancy (1 + 1) in a system where two UPMs are paralleled
together and the load is less than the supporting capability of one of the UPMs. The system
is paralleled for capacity (2 + 0) if both UPMs in a system are required to support the load.
A parallel capacity system can also be redundant (2 + 1), as long as there is always one or
more UPMs online than required to support the load.
7.3.1 Multiple Module Parallel System Modes
Similar to the single module system, the Powerware 9390 UPS parallel system supports a
critical load in three different modes of operation. The standard operation modes are:
In Normal mode, the paralleled UPMs supply the critical load with clean, filtered power.
Each UPM battery charger also provides charging current for the battery if needed.
In Battery mode, the battery provides DC power, which maintains UPM operation. The
UPM batteries supports the critical load.
In Bypass mode, the critical load is directly supported by utility power through the
continuous-duty static bypass switch in each UPM.
The UPMs continually monitor themselves and the incoming utility power, and
automatically switch between these modes as required, without operator intervention,
except when manually switching to Bypass mode. The sophisticated detection and
switching logic inside the UPMs ensures that operating mode changes are automatic and
transparent to the critical load, while internal monitoring systems indicate the current
mode of operation. The UPMs switch operating modes in response to these system events:
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.
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 12, "Responding
to System Events."
To assist in developing an understanding of the parallel systems modes of operation,
review and understand thoroughly the single module modes of operation
The following paragraphs describe the differences in the three parallel system operating
modes, using block diagrams to show the power flow during each mode of operation.
7-10
Powerware
9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev C
®
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