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Understanding UPS Operation
7-2
Powerware
®
9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev C
If utility power is interrupted or falls outside the parameters specified in Chapter 15,
“Product Specifications,” the UPS uses a backup battery supply to maintain power to the
critical load for a specified period of time or until the utility power returns. For extended
power outages, the UPS allows you to either transfer to an alternative power system (such
as a g enerator) or shut down your critical load in an orderly manner.
The emergency bypass consists of a continuous-duty static switch and backfeed protection
contactor K5. The backfeed protection contactor is located in series with the static switch.
For manual transfers to bypass, the static switch is also used. The static switch is armed and
ready during both types of transfers.
The operation of the UPS system is described in greater detail in the following paragraphs.
TheUPSmodulemaybeconfiguredforstandalone,singlemodule,ReverseTransfer(RT)
operation or multiple module, parallel redundant and/or parallel capacity operation (see
paragraphs 7.2 and 7.3).
7.2 Single Module Reverse Transfer (RT)
Asinglemoduleoperatesindependentlytosupportanappliedloadfromtheinverter,
providing conditioned and uninterruptible AC power to the critical load from the output of
the module. During an outage, the inverter continues to operate, supporting power to the
load from the battery supply. If the unit requires service, applied loads are transferred to
the internal bypass, continuous-duty static switch either automatically or manually. With
the exception of a b attery cabinet, no other cabinets or equipment are required for the
single module to successfully support its applied loads.
7.2.1 Single Module RT Modes
The Powerware 9390 UPS supports a critical load in three different modes of operation.
The UPS can automatically use all three modes, as required. The standard operation
modes are:
Ī In Normal mode, the critical load is supplied by the inverter, which derives its power
from rectified utility AC power. In this mode, the battery charger also provides charging
current for the battery, if needed.
Ī In Battery mode, the battery provides DC power, which maintains inverter operation.
The battery supports the critical load.
Ī In Bypass mode, the critical load is directly supported by utility power.