GE GCX51A - Description; Application

GEI
-
98328
DIRECTIONAL
DISTANCE
(
REACTANCE
)
RELAYS
TYPE
GCX
51
DESCRIPTION
The
Type
GCX
51
A
and
GCX
51
B
relays
are
single
-
phase
,
three
-
zone
phase
-
distance
relays
.
The
first
-
and
second
-
zone
distance
measurements
are
made
by
a
unit
having
a
reactance
(
or
OHM
)
type
of
characteristic
,
while
the
third
zone
has
a
directional
MHO
characteristic
.
The
GCX
51
A
and
51
B
relays
are
identical
except
that
the
GCX
51
B
contains
an
instantaneous
overcurrent
fault
detector
while
the
GCX
51
A
does
not
.
Three
type
-
GCX
51
relays
plus
a
suitable
RPM
or
SAM
timing
relay
will
provide
three
-
step
directional
distance
protection
against
three
-
phase
,
phase
-
to
-
phase
,
and
double
-
phase
-
to
-
ground
faults
on
a
transmission
line
,
conjunction
with
other
relays
and
pilot
channels
to
provide
high
-
speed
protection
in
transferred
-
tripping
and
directional
-
comparison
schemes
.
Each
GCX
51
has
one
target
seal
-
in
unit
and
comes
in
an
L
2
case
.
The
R
-
X
characteristics
of
these
relays
are
shown
in
the
R
-
X
diagram
of
Figure
5
.
They
are
also
used
in
APPLICATION
The
type
GCX
51
A
and
GCX
51
B
relays
,
because
of
the
reactance
characteristics
of
their
first
and
second
zones
,
are
particularly
well
suited
for
the
protection
of
circuits
where
arc
resistance
is
apt
to
be
a
problem
.
Since
the
arc
resistance
in
a
fault
is
directly
related
to
the
length
of
the
arc
and
inversely
to
the
current
,
arc
resistance
is
independent
of
line
length
.
Thus
,
arc
resistance
becomes
a
more
significant
part
of
the
total
impedance
from
the
relay
to
the
fault
as
the
protected
line
length
gets
shorter
.
It
is
for
this
reason
that
the
GCX
type
of
characteristic
is
ideally
suited
for
the
protection
of
short
transmission
lines
.
However
,
the
GCX
51
relays
may
also
be
applied
on
longer
lines
if
the
range
of
the
relay
permits
the
required
reach
settings
.
It
will
be
noted
in
the
section
on
RATINGS
that
the
reactance
unit
in
each
GCX
51
relay
provides
three
basic
minimum
-
reach
settings
,
readily
selected
by
means
of
a
tap
link
at
the
front
of
the
relay
.
In
general
,
when
setting
these
units
for
a
given
reach
,
it
is
desirable
to
use
the
highest
basic
reach
tap
that
will
accommodate
the
required
first
-
zone
reach
setting
.
For
example
,
if
a
0.75
ohm
setting
is
required
for
the
first
zone
of
a
standard
reach
relay
,
the
0.5
ohm
basic
reach
tap
should
be
used
rather
than
the
0.25
ohm
tap
.
It
is
not
recommended
that
the
OHM
unit
tap
leads
be
set
for
less
than
10
%
.
These
instructions
do
not
purport
to
cover
all
details
or
variations
in
equipment
nor
provide
for
every
possible
contingency
to
be
met
in
connection
with
installation
,
operation
or
maintenance
.
Should
further
information
be
desired
or
should
particular
problems
arise
which
are
not
covered
sufficiently
for
the
purchaser
’
s
purposes
,
the
matter
should
be
referred
to
the
General
Electric
Company
.
To
the
extent
required
the
products
described
herein
meet
applicable
ANSI
,
IEEE
and
NEMA
standards
;
but
no
such
assurance
is
given
with
respect
to
local
codes
and
ordinances
because
they
vary
greatly
.
3
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