UNDERSTANDING UPS OPERATION
Eaton 9395 UPS (225–275 kVA) Installation and Operation Manual S 164201683 Rev 3 www.eaton.com/powerquality
6-2
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, 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 UPS to successfully support its applied loads.
6.2.1 Modes
The Eaton 9395 UPS supports a critical load in five different modes of operation:
NOTE The Variable Module Management System and Energy Saver System modes are mutually exclusive.
S 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.
S In Energy Saver System (ESS) 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.
S In Variable Module Management System (VMMS) 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.
S In Bypass mode, the critical load is directly supported by utility power.
S 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 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 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 or boost DC
converter, depending on the system voltage and the size of the battery string
attached to the unit.
The battery converter derives its input from the regulated DC output of the rectifier
and provides either a boosted or 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.
To Next Page
Loading...
