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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