GE GCX51A - Ratings

GE
1
-
98328
The
third
zone
MHO
unit
of
these
relays
is
adjusted
at
the
factory
to
have
an
angle
of
maximum
torque
of
60
°
.
Athough
this
can
be
adjusted
up
to
75
°
,
it is
desirable
to
retain
the
60
°
setting
to
obtain maximum
arc
resistance accommodation
for
first
zone
faults close
to
the
relay
location
.
It
is
not
recommended that the
MHO
unit
tap
leads
be
set
for less
than
25
%
.
The
MHO
unit
reach
setting
may
be
subject
to
further
limitations
as
described
in
Appendix
I
.
Table
I
shows
the
minimum
currents
required
in
the
relay
for
three
-
phase
faults
at
the
remote
end
of
the
protected
line
.
These
values
of
current
were
determined
by
tests
of
all
conditions
of fault
locations
,
of
MHO
and
OHM
unit
coordination
,
and
of
proper
unit
contact
action
to
determine
the
final limitation
for
positive
relay
operation
for
any
multi
-
phase
fault
on
the
line
.
TABLE
I
Min
.
Three
-
Phase
Fault
Current
Secondary
Amperes
Basic
Tap
Setting
Short
-
Reach
Relay
0.1
ohms
0.2
ohms
0.4
ohms
16
-
Amperes
10
-
Amperes
10
-
Amperes
Standard
-
Reach
Relay
0.25
ohms
0.50
ohms
1.00
ohms
6
-
Amperes
5
-
Amperes
4
-
Amperes
Because
they
have
no
significant
transient
overreach
,
the
first
-
zone
units
of
the
GCX
51
relays
may
be
set
for
90
%
of the
distance
to
the
nearest remote
terminal
.
The
second
-
zone
units
should
be
set
to
reach
at
least
110
%
of the
distance
to
the
farthest
remote
terminal
(
including
the
effects
of
infeed
if
present
)
.
The
third
-
zone
MHO
units
should
be
set
to
reach
sufficiently
farther
than
the
second
-
zone
units
to
provide
for
accommodating
arc
resistance
at
the
second
-
zone
balance
point
.
The
third
-
zone
MHO
units
sometimes
are
used
to
obtain
back
-
up
protection
for
faults
on
remote
line sections
.
However
,
it
is
not
good
practice
to
set
the
MHO
unit
to
reach
any
farther than
is
necessary
.
The
overcurrent
fault
detector
in
the
GCX
51
B
relays
should
always
be
set
to
pick
up
no
lower than
115
%
of
maximum
load
current
.
These fault
detector
units
are
not
designed
to
operate
continuously
in
the
picked
-
up
position
.
For
information
on
settings
see
the
section
on
CALCULATIONS
OF
SETTINGS
.
For
typical
external
connections
in
a
three
-
step
distance
scheme
see
Figure
3
.
RATINGS
The
Type
GCX
51
A
and
GCX
51
B
relays
covered
by
these
instructions
are
available
for
120
volts
,
5
amperes
,
50
/
60
cycle
rating
.
The
1
-
second
current
rating
is
225
amperes
.
The
DC
control
voltage
of
48
/
125
/
250
is
selected
by
a
link
setting
on
the
front
of
the
relay
.
The
basic
minimum
reach
and
adjustment
range
for
the
OHM
and
MHO
units
of the
standard
-
reach and short
-
reach forms
of the
relay
are
given
in
Table
II
.
4
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