Powerware 9395 UPS 10001100 kVA - Manuel (Page 106)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9395 UPS (1000–1100 kVA) Installation and Operation Manual S 164201764 Rev 1 www.powerware.com 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 Powerware 9395 UPS supports a critical load in three different modes of
operation:
S
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.
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 UPS can automatically use all three modes, as required. 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.
6.2.2 Normal Mode
Figure 6-2 shows the path of electrical power through the UPS system when the UPS
is operating in Normal 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 Normal,"
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.
The inverter produces a three−phase AC output to a customer’s load without the use
of a transformer. The inverter derives regulated DC from the rectifier and uses IGBT
devices and pulse−width modulation (PWM) to produce a regulated and filtered AC
output. The AC output of the inverter is delivered to the system output through the
output contactor K3.
If the utility AC power is interrupted or is out of specification, the UPS automatically
switches to Battery mode to support the critical load without interruption. When utility
power returns, the UPS returns to Normal mode.