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Principles of Operation
Y
v
External Power
Supply
Static
Trip lllC/CP/CPX model trip
units
require external
15V
dc
control power for the communications microprocessor.
This
allows
communication
with the
trip
unit
during
all load
current
conditions,
even with the
circuit
breaker switched
off.
lnternal
isolation prevents wiring faults from damaging the
trip
unit's
protective
circuits.
PT
Module
A special purpose
potential transformer
assembly
is used to
supply voltage signals
to
Static Trip lllCP/CPX model trip units
and provide
isolation
from the primary circuits,
Class
CC
1A
600V fuses
are
used
to
protect against internal
PT module
faults.
The
PT
modules
are
encapsulated
in
polymeric material
to
protect
the
transformer
windings
and withstand mechanical
vibration when mounted directly
on the
circuit
breaker, The
PT
module primary inputs
are
from
the
three phases plus neutral.
For
3-wire systems, the neutral
conductor input
is not used.
BDU Breaker
Display
Unit
The
BDU
accessory provides a local
means
of reading data
from
and
programming Static
Trip
llIC/CP/CPX
model
trip
units.
lt
contains its own microprocessor which controls
the
display and communicates with the
trip
unit using
the
local
BDU
communication port.
Power
to operate the
LED
display
and
microprocessor
circuitry
is
derived from
the trip
unit
through
this same port.
lsolated lnput/Output
lnput for
a
52b breaker
position switch
and
outputs for Alarm
(output
1)
and
Close Breaker (output 2) are
optically
isolated
to
protectthetrip
unit's internal protection
circuitsfrom
external
wiring faults. These outputs are
rated
I00mA
12Y and
require
an
interposing
relay
to
integrate these
control signals
into the
desired
breaker wiring.
Shadow
Protection
The
overcurrent protection functions
are enhanced
by
the
communications microprocessor,
The
protection micropro-
cessor operates totally independent of the communications
and
metering
functions.
Should
communications
or metering
processing
fail, the
protection functions will
remain
fully opera-
tional,
However,
the communications microprocessor
is pro-
grammed
to
provide backup or "shadow" fault protection.
The
"shadow" protection
curve is defined
by
pickup and
delay
values slightly above the highest available settings for
Long
Time and
Short Time
functions, In
the
unlikely
event
of
a
protection microprocessor failure,
the
communications micro-
processor
will
execute the
overcurrent protection
functions.
Long
Time
o
E
Current
Short
Shadow Protection
Y
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