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 support the critical load.
In Bypass mode, the critical load is directly supported by utility power through the
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 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 12, “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 paragraphs describe the differences in the three parallel system operating modes, using block diagrams to show the power flow during each mode of operation.
