GE GCX51A - Operating Time

GEI
-
98328
The
tap
setting
required
to
protect
a
zone
X
ohms
long
,
where
X
is
the
positive
-
phase
-
sequence
reactance
(
phase
-
to
-
neutral
)
expressed
in
secondary
ohms
,
is
determined
by
the
following
equation
:
Output
Tap
Setting
(
%
)
=
f
Input
Tap
Setting
(
%
)
}
fBasic
Min
.
Ohms
)
X
For
a
numerical
example
of
the
determination
of
the
OHM
and
MHO
unit
settings
,
refer
to
the
section
on
CALCULATIONS
OF
SETTINGS
.
The
purpose
of
the
OHM
unit
in
the
GCX
51
relays
is
to
provide
an
accurate
measurement
of
the
distance
to
a
fault
and
to
close
its
contacts
if
the
fault
lies
within
the
first
or
second
zone
protected
by
the
relay
.
The
overreach
of
the
OHM
unit
from
transient
offset
of
the
fault
current
is
very
small
,
even
with
highly
lagging
line
impedances
,
and
can
be
neglected
for
relay
settings
within
the
recommended
ranges
.
Operating
Time
The
operating
time
of
the
Type
GCX
51
relay
is
determined
by
a
number
of
factors
such
as
basic
minimum
reach
of
the
OHM
and
MHO
units
,
fault
-
current
magnitude
,
ratio
of
fault
impedance
to
relay
reach
,
and
whether
relay
voltage
prior
to
the
fault
is
at
rated
120
volts
or
is
zero
(
0
)
.
A
series
of
figures
is
included
at
the
rear
of
the
book
showing
operating
time
of
the
MHO
unit
and
overall
operating
time
of
the
relay
for
a
number
of
typical
conditions
.
The
operating
time
of
the
MHO
unit
is
given
separately
because
this
unit
is
frequently
used
for
the
carrier
-
stop
function
in
directional
comparison
carrier
schemes
.
The
time
-
curve
figures
are
listed
in
Table
IV
for
the
MHO
unit
alone
and
in
Table
V
for
the
relay
.
TABLE
IV
Time
Curves
for
MHO
Unit
Alone
Volts
Prior
to
Fault
Basic
Min
.
Reach
(
MHO
Unit
)
Figure
#
Relay
lb
120
1.0
ohm
Short
Reach
Stand
.
Reach
0
16
1.0
ohm
17
120
2.5
ohm
18
0
2.5
ohm
In
each
figure
it
will
be
noted
that
time
curves
are
given
for
three
ratios
of
fault
impedance
to
relay
reach
setting
.
In
the
case
of
the
figures
for
the
zero
-
voltage
condition
,
an
additional
curve
(
shown
dotted
)
is
also
given
for
a
4
-
volt
resistive
fault
condition
.
In
all
cases
,
the
E
?
and
/
or
the
No
.
1
taps
were
in
the
100
%
position
and
the
MHO
unit
angle
of
maximum
torque
was
set
at
60
°
lag
.
9
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