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The UPS continually monitors itself and the incoming utility power, and automatically
switches between these modes as required, without operator intervention. The
sophisticated detection and switching logic inside the UPS ensures that operating mode
changes are automatic and transparent to the critical load, while internal monitoring
systems indicate the current mode of operation. The UPS switches operating modes in
response to these system events:
System events, alarm horns, and indicator lights are described in Chapter 12, "Responding
to System Events."
The following paragraphs describe the differences in the three UPS operating modes, using
block diagrams to show the power flow during each mode of operation.
EATON Powerware
9390 UPS (100–160 kVA) Installation and Operation Manual S 164201554 Rev E powerware.com
®
A command is an intervention that is externally initiated by an operator or by some site
action. A command causes the UPS 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 operator intervention.
Understanding UPS Operation
7-3
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