During a utility
power
failure, the rectifier no longer has an AC utility
source
from which to supply the DC
output
voltage
required
to
support
the inv
erter
.
The input
contactor opens
and the
battery inst
ant
aneously supplies energy
to the
battery con
v
erter
.
The
converter boosts
the voltage so that the inverter can
support
the customer's
load
without interruption.
If
bypass
is
common
with the rectifier input, the
backfeed protection contactor
also
opens.
The
opening
of the input and the optional
backfeed protection contactors pre
v
ent system
voltages
from
bleeding
backwards through
the static
switch
and rectifier
snubber components
to
the
utility
source.
If the input
power
fails to return or is not within the
acceptance windows required
for normal
operation,
the
battery
continues discharging
until a DC voltage level is
reached where
the inverter
output
can no
longer
support
the
connected
loads. When this
event occurs,
the UPS
issues another
set of audible and visual
alarms
indicating
SHUTDOWN IMMINENT.
Unless
the rectifier has a valid AC input soon, the
output
can be
supported
for only two
minutes before
the
output
of the
system shuts down.
If the
bypass source
is available, the
UPS
transfers
to
bypass
instead
of
shutting do
wn.
If at any time during the
battery discharge
the input
power becomes
available again, the input and the
bac
kf
eed
protection contactors
close and the rectifier
begins
to supply DC
current
to the
converter
and
inverter.
At
this
point,
the unit
returns
to Normal
mode. Depending
on the total load and the duration of the
battery disc
harge,
battery
current
limit alarms may be
seen
for a short time due to the
current required
to
recharge
the
bat
ter
y
.
5.3 Single
UPS Unit System One line
Configurations
The
system
one line
drawings
in this
section show
the simplified internal
structure
of the UPS,
battery
supply
,
and basic
maintenance
b
ypass.
Oneline
Drawing
V
oltage
UPS
Model Input Output
System
T
ype
See Figure
5-5
See Tab 9-1
for
Model
380/400/415 380/400/415
Single Reverse
T
ransfer
UPS with External
Battery
Eaton 93E MK2 UPS (10-40kVA, 380/400/415V) Installation and Operation
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