Powerware 9390 UPS 100160 kVA - Manual (Page 54)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9390 UPS (20–80 kVA) Installation and Operation Manual S 164201603 Rev 2 www.powerware.com 7-2
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 UPS module may be configured for standalone, single module, Reverse Transfer
(RT) operation or multiple module, parallel redundant and/or parallel capacity operation
(see paragraphs 7.1 and 7.2).
7.1 Single Module Reverse Transfer (RT)
A single module operates independently to support an applied load from the inverter,
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 battery cabinet, no other cabinets or equipment
are required for the single module to successfully support its applied loads.
7.1.1 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:
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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.
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Battery mode – The battery provides DC power, which maintains inverter operation.
The battery supports the critical load.
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Bypass mode – The critical load is directly supported by utility power.
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:
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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.
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A notice is a minor system event that may or may not require attention.
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An alarm is a system event that requires immediate operator intervention.
System events, alarm horns, and indicator lights are described in Chapter 11,
“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.