Ups Modes - Powerware 9390 Installation & Operation Manual

Understanding UPS Operation
If utility power is interrupted or falls outside the parameters specified in Chapter 14,
"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 generator) 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.

6.2 UPS Modes

The UPS system functions automatically to supply AC electrical power to the critical load.
There are three standard operation modes:
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.
In Battery mode, the battery provides DC power, which maintains inverter operation.
The battery supports the critical load.
In 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, with no operator intervention. The
sophisticated detection and switching logic inside the UPS ensures that operating mode
changes are automatic and transparent to the critical load. The UPS switches 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 UPS to switch operating modes; it usually does not
require any further action by you.
A notice is a minor system event that may or may not require your attention.
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 descriptions provide the differences in UPS operating modes.
6-2
Powerware 9390 UPS (40–80 kVA) Installation and Operation Manual S 164201535 Rev A
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