UNDERSTANDING UPS OPERATION
Eaton
Power Xpert 9395P UPS (300 kVA, 300 kW) Installation and Operation Manual
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P-164000563 Rev 1
www.eaton.com/powerquality
6-2
On a UPS configured as an Input Output Module (IOM), bypass circuitry is not
installed. This configuration is primarily used in multiple UPS parallel systems that do
not need a bypass for each UPS and use a separate System Bypass Module (SBM) to
provide system bypass capabilities.
6.2
Single UPS
A single UPS 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 either automatically or manually. With the exception
of a battery cabinet, no other cabinets or equipment are required for the single UPS to
successfully support its applied loads.
6.2.1
Modes
The Eaton 9395P UPS supports a critical load in five different modes of operation:
NOTE
Variable Module Management System and Energy Saver modes are mutually exclusive.
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In Online 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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In Energy Saver mode, commercial AC power is supplied directly to the critical load
through the continuous static switch and transfers automatically to Online mode if
an abnormal condition is detected. The Energy Saver mode requires a UPS with a
continuous static switch.
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In Variable Module Management System mode, the UPS operates as a traditional
double-conversion UPS, but selectively shifts the load to fewer UPMs to increase
the efficiency of the UPS.
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In Bypass mode, the critical load is directly supported by utility power.
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In Battery mode, the battery provides DC power, which maintains inverter
operation. The battery supports the critical load.
The following paragraphs describe the differences in the five UPS operating modes,
using block diagrams to show the power flow during each mode of operation.
6.2.2
Online Mode
Figure 6‐2 shows the path of electrical power through the UPS system when the UPS
is operating in Online
mode.
During normal UPS system operation, power for the system is derived from a utility
input source through the rectifier input contactor K1. The front panel displays
“Online,” indicating the incoming power is within voltage and frequency acceptance
windows. Three-phase AC input power is converted to DC using IGBT devices to
produce a regulated DC voltage to the inverter. When contactor K2 is closed the
battery is charged directly from the regulated rectifier output through a buck DC
converter.
The battery converter derives its input from the regulated DC output of the rectifier
and provides a bucked regulated DC voltage charge current to the battery. The battery
is always connected to the UPS and ready to support the inverter should the utility
input become unavailable.
