Powerware 9395 UPS and Plus 1 UPS 650825 kVA - Manual (Page 114)

UNDERSTANDING UPS OPERATION
EATON Powerware ® 9395 UPS (650–825 kVA) Installation and Operation Manual S 164201725 Rev 2 www.powerware.com 6−2
The emergency bypass consists of a momentary−duty static switch, a wraparound
bypass breaker, and a backfeed protection contactor K5. The bypass breaker is
located in parallel with the static switch. The backfeed protection contactor is located
in series with the static switch. Bypass breaker CB4 is used for manual transfers to
bypass without using the static switch. The static switch is armed and ready during
both types of transfers.
On an 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, 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.