Battery
5.2.4
Bypass
Mode
CAUTION
The critical load is not
protected
from voltage or
frequency fluctuations
or
power outages while
the UPS is in
Bypass
mode.
The UPS
automatically switches
to
Bypass mode
if it
detects
an
overload,
load fault, or internal failure.
T
he
UPS can also be
transferred
from Normal
mode
to
Bypass mode
manually. The
bypass source supplies
the
commercial
AC
power
to the load directly. Figure 5-3
shows
the path of electrical
power through
the
UPS
system when operating
in
Bypass
mode.
In
Bypass mode,
the
output
of the
system
is provided with
three-phase
AC
power
directly from the
sy
stem
input. While in this
mode,
the
output
of the
system
is not
protected
from voltage or
frequency fluctuations or
power outages
from the
source. Some power
line filtering and spike
protection
is provided to the load but
no
active
power conditioning
or
battery support
is available to the
output
of the
system
in the
Bypass mode of
operation.
The internal
bypass
is
comprised
of a
solid-state, silicon-controlled
rectifier
(SCR)
continuous
static
switch, and
an optional
backfeed protection
cont
actor.
The static
switch
is
used instantaneously anytime
the inverter
is
unable to
support
the applied load. The
continuous
static
switch
is wired in
series
with the
backfeed protection
contactor
(if
fitted), and
together
they are wired in parallel with the rectifier and inv
erter
.
The static
switch,
being an
electronically-controlled
device, can be
turned
on
immediately
to pick up the
load
from the inverter while inverter
output contactor opens
to isolate the inv
erter
.
The
backfeed protection
contactor
(if
fitted) is normally
closed,
ready to
support
the static
switch unless
the
bypass
input
source
becomes
una
v
ailable.
If the UPS
transfers
to
Bypass mode
from Normal
mode
due to any
reason
other than
operator
inter
v
ention,
the UPS
automatically
attempts
to
transfer
back to Normal
mode
(up to
three times
within a ten
minute
period). The fourth
transfer
locks the critical load to the
bypass source
and
requires operator intervention
to
transf
er
.
Bypass
Input
Bypass Switch (Optional Dual Input)
Static
Rectifier
Input
Input
Switch
Input
Rectifier
Switch
Inverter
Output
Relay
Output
Relay
Battery
Converter
Switch
Relay
Closed
Open
Battery
Relay
Main Power Flow
Trickle
Current
Energized
De-Energized
Figure
5-3.
Path of Current Through
the UPS in standard Bypass
Mode
Eaton 93E MK2 UPS (10-40kVA, 380/400/415V) Installation and Operation
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