GE GCX51A User manual

GEI
-
98328
J
INSTRUCTIONS
DIRECTIONAL
DISTANCE
(
REACTANCE
RELAY
)
TYPES
GCX
51
A
Forms
11
and
up
GCX
51
B
Forms
11
and
up
GENERAL
ELECTRIC
Courtesy of NationalSwitchgear.com

GE
1
-
98328
TABLE
OF CONTENTS
PAGE
3
DESCRIPTION
. . ..
APPLICATION
. .. .
RATINGS
OPERATING
PRINCIPLES
MHO
Unit
. . .
OHM
Unit
. . .
CHARACTERISTICS
.
.
MHO
Unit
.
..
OHM
Unit
.
.
.
3
4
6
6
6
7
7
8
9
Operating
Time
Vernier
Adjustment
for
Low
Tap
Settings
OHM
Unit
Transfer
Auxiliary
10
10
11
BURDENS
CALCULATION
OF SETTINGS
CONSTRUCTION
ACCEPTANCE
TESTS
Visual
Inspection
Mechanical
Inspection
Electrical
Checks
MHO
Unit
Checks
Control
Spring
Adjustment
Ohmic
Reach
Angle
-
of
-
Maximum
-
Torque
Check
....
OHM
Unit
Checks
Control
-
Spring
Adjustment
Ohmic
Reach
and
Angle
of
Maximum
Torque
Other
Checks
and
Tests
OHM
-
Unit
Transfer
Relay
(
OX
)
. . . .
Target
/
Seal
-
in
Unit
INSTALLATION
PROCEDURE
Location
Mounting
Connections
Visual
Inspection
Mechanical
Inspection
Electrical
Check
Tests
on
Induction
Units
Testing
the
OHM
Unit
Testing
the
MHO
Unit
Other Checks
and
Tests
Overall
Tests
PERIODIC CHECKS
AND
ROUTINE
MAINTENANCE
.
.
.
Contact
Cleaning
SERVICING
MHO
UNIT
12
14
15
15
16
16
16
16
17
17
18
18
18
18
18
19
19
19
19
19
19
19
20
20
21
24
25
26
26
26
26
26
Control
-
Spring
Adjustment
Ohmic
Reach
Adjustment
Angle
of
Maximum
Torque
27
27
28
OHM
UNIT
28
Control
-
Spring
Adjustment
Reach
and
Angle
-
of
-
Maximum
-
Torque
Adjustment
28
29
RENEWAL
PARTS
LIST OF FIGURES
APPENDIX
I
30
48
2
Courtesy of NationalSwitchgear.com

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
Courtesy of NationalSwitchgear.com

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
Courtesy of NationalSwitchgear.com

GE
1
-
98328
TABLE
II
MHO
UNIT
OHM
UNIT
**
ANGLL
Oh
MAX
.
TORQUE
RANGE
(
0
-
N
OHMS
)
RANGE
(
0
-
N
OHMS
)
BASIC
MIN
.
REACH
(
0
-
N
OHMS
)
BASIC
MIN
.
REACH
*
(
0
-
N
OHMS
)
RELAY
ms
O
.
l
/
O
.
2
/
0.4
174
0.1
/
4
T
Short
Reach
2.5
/
10
0.25
/
0.5
/
1.0
0.25
/
10
600
2.5
Standard
Reach
*
Adjustment
link
is
set
at
the
0.2
or
0.5
basic
min
.
reach
prior
to
shipment
.
The
angle
of
maximum
torque
of
the
MHO
unit
can
be
adjusted
up
to
75
°
with
resulting
increase
in
reach
to
approximately
120
%
of
the
reach
at
the
60
°
angle
of
maximum
torque
.
It
will
be
noted
that
for
each
relay
three
basic
minimum
reach
settings
are
listed
for
the
OHM
unit
.
Selection
of
the
desired
basic
minimum
reach
is
made
by
means
of
two
captive
tap
screws
on
a
tap
block
at
the
front
of
the
relay
.
The
reach
settings
of
the
OHM
and
the
MHO
units
can
be
adjusted
in
one
percent
(
1
%
)
steps
by
means
of
auto
-
transformer
tap
leads
on
the
tap
block
at
the
right
side
of
the
relay
.
First
-
zone
reach
of
the
OHM
unit
is
determined
by
the
No
.
1
leads
second
-
zone
reach
by
the
No
.
2
leads
,
and
the
reach
of
the
MHO
unit
,
by
the
L
leads
.
E
*
The
GCX
51
B
relay
includes
an
instantaneous
overcurrent
unit
identified
as
OC
on
The
short
-
reach
form
of
the
GCX
51
is
the
internal
-
connection
diagram
,
Figure
8
.
normally
furnished
with
an
OC
unit
having
a
4
-
16
ampere
calibration
range
,
standard
-
reach
form
is
available
with
OC
calibration
ranges
of
4
-
16
,
2
-
8
or
1
-
4
The
amperes
.
The
contacts
of
the
GCX
51
relays
will
close
and
carry
momentarily
30
amperes
DC
.
However
,
the
circuit
-
breaker
trip
circuit
must
be
opened
by
an
auxiliary
switch
contact
or
other
suitable
means
,
since
the
relay
contacts
have
no
interrupting
rating
.
The
0.6
/
2
ampere
target
seal
-
in
unit
used
in
the
GCX
51
relays
has
ratings
as
shown
in
Table
III
.
TABLE
III
TARGET
SEAL
-
IN
UNIT
0.6
Amp
lap
2.0
Amp
lap
Minimum
Operating
Carry
Continuously
Carry
30
Amps
for
Carry
10
Amps
for
DC
Resistance
60
Cycle
Impedance
2.0
amps
3.5
amps
4
secs
.
30
secs
.
0.13
ohms
0.53
ohms
0.6
amps
1.5
amps
0.3
secs
.
4
secs
.
0.6
ohms
6
ohms
5
Courtesy of NationalSwitchgear.com

GEI
-
98328
OPERATING
PRINCIPLES
MHO
Unit
The
MHO
unit
of
the
Type
GCX
51
relays
is
of the
four
-
pole
induction
cylinder
construction
(
see
Figure
14
)
with
schematic
connections
as
shown
in
Figure
4
.
The
two
side
poles
,
energized
with
phase
-
to
-
phase
voltage
,
produce
the
polarizing
flux
.
The flux
in
the
front
pole
,
energized
with
a
percentage
of the
same
phase
-
to
-
phase
voltage
,
interacts with
the
polarizing
flux
to
produce
restraint
torque
.
The
flux
in
the
rear
pole
,
energized
with
the
two
line
currents
associated
with
the
same
phase
-
to
-
phase
voltage
,
interacts
with
the
polarizing
flux
to
produce
the
operating
torque
.
The
torque
at
the
balance
point
can
therefore
be
expressed
by
the
following
equation
:
T
=
0
=
El
cos
(
0
-
0
)
-
KE
2
where
:
E
=
The
phase
-
to
-
phase voltage
(
E
12
)
I
=
The
delta
current
(
Ii
-
I
2
)
0
=
Angle
of
maximum
torque
of
the
unit
0
=
Power
factor
angle
of
fault
impedance
K
=
Design
constant
Dividing
through
by
E
2
and
transposing
,
the
equation
reduces
to
the
following
expression
in
terms
of
impedance
:
1
Y
cos
(
0
-
0
)
=
K
cos
(
0
-
0
)
=
K
Thus the
unit
will
pick
up
at
a
constant
component
of
admittance
at
a
fixed
angle
,
depending
on
the
angle
of
maximum
torque
.
Hence
the
name
MHO
unit
.
or
Z
OHM
Unit
The
OHM
unit
of the
GCX
51
relays
is
also of
the four
-
pole
induction
cylinder
construction
(
see
Figure
14
)
with
schematic
connections
as
shown
in
Figure
4
.
front and
back
poles
,
energized
with
delta
current
,
produce
the
polarizing
flux
.
The
side
poles
are
energized
with
a
voltage
equal
to
the
difference
between
the
operating
quantity
,
IZT
and the
restraint
voltage
,
E
,
where
I
is
the
delta
current
and
ZT
is
the
transfer
impedance
of
the
transactor
.
Torque
on
the
unit
results
from
interaction
between
the
net
flux
in
the
side
and the
polarizing
flux
in
the
front
and
rear
poles
,
and
at
the
balance
point
can
be
expressed
by
the
following
equation
:
T
=
0
=
Kl
(
IZT
-
E
)
sin
p
The
where
:
E
=
phase
-
to
-
phase voltage
(
E
^
)
I
=
delta
current
(
Ii
-
I
2
)
Zj
=
transfer
impedance
of
transactor
(
design
constant
)
p
=
angle
between
I
and
(
IZj
-
E
)
K
=
design
constant
6
Courtesy of NationalSwitchgear.com

GEI
-
98328
By
means
of
trigonometric
relations
,
the
above
equation
can
be
reduced
to
:
(
KI
)
(
IZT
)
sin
0
-
KI
(
E
)
sin
0
=
0
where
:
0
=
angle
between
I
and
IZj
(
i
.
e
.
the
transactor
angle
,
a
design
constant
)
0
=
angle
between
E
and
I
(
i
.
e
.
angle
of
fault
impedance
)
Since
Zj
for
a
particular
transactor
tap
setting
is
also
a
design
constant
,
the
equation
becomes
:
K
'
l
2
=
K
IE
sin
9
—
=
K
"
=
-
I
sin
e
I
K
K
"
=
Z
sin
9
=
XF
Thus
the
unit
will
operate
when
the
fault
reactance
XF
is
less
than
a
constant
determined
by
the
transactor
characteristics
and
tap
setting
.
CHARACTERISTICS
The
operating
characteristics
of
the
OHM
and
MHO
units
in
the
GCX
51
relays
are
best
shown
as
impedance
characteristics
on
an
R
-
X
diagram
.
(
See
Figure
5
)
.
MHO
Unit
The
MHO
unit
has
a
circular
impedance
characteristic
which
passes
through
the
origin
and
has
its
center
on
the
angle
-
of
-
maximum
-
torque
line
of
the
unit
,
basic
minimum
reach
of
the
unit
at
the
angle
of
maximum
torque
(
see
Table
II
under
RATINGS
)
is
obtained
when
the
E
?
restraint
taps
are
on
100
%
.
The
ohmic
reach
can
be
extended
by
reducing
the
percentage
of
the
fault
voltage
applied
to
the
restraint
circuit
,
that
is
by
setting
the
E
?
restraint
taps
on
a
lower
percentage
position
on
the
tap
block
.
The
ohmic
reach
of
the
unit
at
the
transmission
line
angle
,
which
will
usually
differ
from
the
angle
of
maximum
torque
,
can
be
determined
from
the
following
equation
:
Ohmic
Reach
at
Line
Angle
=
(
Input
Tap
)
Zmin
COS
(
9
-
0
)
Tap
Setting
(
%
)
The
where
:
0
=
Angle
of
maximum
torque
of
the
unit
0
=
The
angle
of
the
line
Zmin
-
The
basic
minimum
phase
-
to
-
neutral
ohmic
reach
of
the
unit
Input
tap
setting
in
Percent
(
normally
is
100
except
as
explained
under
"
Vernier
Adjustment
"
on
page
10
)
.
E
2
Tap
Setting
(
%
)
=
the
E
?
or
Voltage
Restraint
Tap
Setting
in
percent
For
E
2
tap
and
input
tap
settings
of
100
%
the
phase
-
to
-
neutral
ohmic
reach
will
be
equal
to
the
basic
minumum
reach
shown
in
Table
II
under
RATINGS
when
the
angles
0
and
0
are
equal
.
Input
Tap
=
7
Courtesy of NationalSwitchgear.com

6
E
1
-
98328
The
primary
purpose
of the
MHO
unit
in
the
type
-
GCX
51
relays
is
to
provide
the
directional
discrimination
that
is
necessary
since
the
OHM
unit
is
inherently
nondirectional
.
The
MHO
unit
directional
characteristic is
such that
it
will
operate
correctly
for
either
forward
or reverse
faults
at
voltages
down
to
1
%
of
rated
voltage
over a
current
range
of
5
to
60
amperes
.
A
secondary
purpose
of
the
MHO
unit is
to
measure
fault
impedance
for
the
third
zone
of
protection
.
At
reduced
voltage
,
the
ohmic
value
at
which
the
MHO
unit
will
operate
may
be
somewhat
lower
than
its
calculated
value
.
This
"
pullback
"
or
reduction
in
reach
is
shown
in
Figure
6
for
the
1.0
ohm
MHO
unit
used
in
the
short
-
reach
relay
,
or
in
Figure
7
for
the
2.5
ohm
MHO
unit
used
in
the
standard
-
reach
relay
.
The
percentage
of
relay
reach
for
a
constant
tap
setting
is
expressed
as
a
function
of the three
-
phase
fault
current
,
I
30
,
for
various ohmic
reach
settings
.
The
MHO
unit
will
operate
for all
points
to
the
right
of
the
curves
.
The
static
curves
of
Figures
6
and
7
were
determined
by
tests
performed
with
no
voltage
supplied
to
the
relay
before the
fault
was
applied
.
The
dynamic
curves were
obtained
with
full
rated
voltage
of
120
volts
supplied
to
the
relay
before
the fault
was
applied
.
These
dynamic
curves
illustrate
the
effect
of
the
MHO
unit
memory
action
,
which
maintains
the
polarizing
voltage
on
the
unit
for
a
few
cycles
after
the
inception
of the
fault
.
This
memory
action
is
particularly
effective
at
low
voltage
levels
where
it
enables
the
MHO
unit
to
operate
for
low
fault
currents
.
This
can
be
most
forcefully
illustrated
for
a zero
-
voltage
fault
by
referring
to
Figure
7
.
A
zero
-
voltage
fault
must
be
right
at
the
relay
bus
and
therefore
,
to
protect
for
this
fault
,
it is
imperative
that
the
relay
reach
zero
percent
(
0
%
)
of
its
setting
.
Figure
7
shows
that the
MHO
unit
,
under
static
conditions
,
will
not
see
a
fault
at
zero
percent
(
0
%
)
of the
relay
setting
regardless
of
the
tap
setting
.
However
,
under
dynamic
conditions
when the
memory
action is
effective
,
Figure
7
shows that
a
2.5
-
ohm
MHO
unit
with
a
100
%
tap
setting
will
pick
up
if
I
30
is
greater
than
2.5
A
.
This is
of
course
a
marginal
condition
.
The
minimum
fault
currents
considered
safe
are
listed
in
Table
I
in
the
APPLICATION
section
.
OHM
Unit
The
OHM
unit
impedance
characteristic
when
represented
on
the
R
-
X
diagram
(
Figure
5
)
is
a
straight
line
parallel
with
the
R
axis
.
The
unit
will
operate
for
fault
impedances
lying
below
its
characteristic
,
and
hence
is
non
-
directional
.
During
normal
conditions
when
load
is
being
transmitted
over
the
protected
line
,
the
voltage
and
current
supplied
to
the
unit
present
an
impedance
that
lies
close
to
the
R
axis since
load
will
be
very
near
unity
power
factor
in
contrast
with
the
reactive
KVA
that
flows
during
fault
conditions
.
An
impedance
near
the
R
axis
will
lie
below the
OHM
unit
characteristic
(
see
Figure
5
)
and hence
the
OHM
unit
contact
will
be
closed
.
This
will
cause
no
trouble
,
however
,
since
the
directional
MHO
unit
contact
will
not
be
closed
for
this
condition
(
see
Figure
3
)
.
The
basic
minimum
reach
of
the
OHM
unit
as
listed
in
Table
II
under
RATINGS
is
obtained
when
the
restraint
tap
leads
are on
100
%
.
The
ohmic
reach
can
be extended
by
setting
the
restraint
tap
leads
on
a
lower
percentage
position
on
the
tap
block
.
The
setting
of the
two
tap
leads marked
No
.
1
determines
the
reach
of
the
instantaneous
or
first
zone
,
and
the
setting
of
the
two
tap
leads marked
No
.
2
determines
the reach of the
intermediate
or
second
zone
.
8
Courtesy of NationalSwitchgear.com

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
Courtesy of NationalSwitchgear.com

GEI
-
98328
TABLE
V
Overall
Time
Curves
for
Relay
Basic
Min
.
Reach
(
MHO
Unit
)
Volts
Prior
to
Fault
Figure
#
Relay
ITU
T
9
OTT
20
0.1
0
120
21
Short
Reach
0.2
0
22
0.2
120
23
0.4
0
24
0.4
75
5775
0.25
170
0
26
120
27
0.5
Standard
Reach
28
0
0.5
120
1.0
29
30
1.0
0
Vernier
Adjustment
for
Low
Tap
Settings
The
input
leads
are
normally
set
at
100
%
but
with
a
high
secondary
-
1
ine
reactance
,
where
the
No
.
1
tap
leads
would
be
set
at
a
low
percentage
,
the
input
connections
may
be varied
by
a
vernier
method
to
obtain
a
closer
setting
,
example
,
if
the
desired
first
zone
reach
is
1.2
ohms and
the basic
minimum
r
-
ach
of
the
OHM
unit is
1.0
ohm
,
with
the
input
on
100
%
the
output
tap
setting
would
be
100
/
1.2
or
83.3
%
,
which
can
be
set
within
0.4
%
.
However
,
if
the
desired
first
zone
reach
were
9.5
ohms
,
the
output
setting
would
be
100
/
9.5
,
or
10.55
%
.
The
nearest
output
tap
would
be
11
%
,
which
is
4
%
off
the
desired
value
.
To
correct
this
,
the
input
leads
can
be
shifted
to
95
%
,
in
which
case
the
output
setting
would
be
95
/
9.5
,
or
10
%
,
which
of
course
can
be
set
exactly
.
For
OHM
Unit
Transfer
Auxiliary
The
OHM
unit
transfer
auxiliary
,
OX
,
is
a
telephone
-
type
relay
whose
coil
and
contacts
are
shown
on
the
right
in
the
internal
-
connection
diagram
of
Figure
8
.
The
unit is mounted
at
the
top
of
the
relay
and
is
used
to
change
the
setting
of
the
OHM
unit
to
provide
a
second
step
of
transmission
-
line
protection
,
controlled
by
the
Type
RPM
or
SAM
timing
relay
as
shown
by
the
external connections
diagram
of
Figure
3
.
The
normally
-
closed
contacts
of
the
transfer
auxiliary
provide
the
circuit
for
instantaneous
tripping
used
for
faults
in
the
first
step
of
line
protection
.
auxiliary
changes
the
setting
of
the
OHM
unit
by
switching
to
the
No
.
2
taps
on
the
autotransformer
,
from
which
a
smaller
potential
is
supplied
to
the
unit
potential
restraint
windings
.
This
extends
the
ohmic
reach
of
the
OHM
unit
and enables
it
to
operate
for
faults
in
the
second
zone
of
transmission
-
line
protection
.
Its
operation
is
If
the
fault is
beyond
the
first
zone
of
protection
,
the
transfer
10
Courtesy of NationalSwitchgear.com

GEI
-
98328
BURDENS
The
maximum
current
burdens
for
the
relay
at
5
amperes
are
listed
in
Table
VI
.
TABLE
VI
P
.
F
.
VA
AMPS CY
.
X
W
R
U
7
T
2
50
87
b
034
8
0732
5
These data
are
for
the
1.0
ohm
minimum
basic
reach
tap
of
the
standard
-
reach
relay
.
The burden
on
the
0.5
and
.
25
taps
,
and
on
the
0.4
,
0.2
and
0.1
ohm
taps
of
the short
-
reach
relay
,
will
be
slightly
lower
.
The
potential
burden
will
vary
with
the
tap
settings
used
for
the
OHM
and
MHO
unit
restraint
circuits and
can
be
calculated
from
the
following
formulae
,
potential
burdens
are
at
120
volts and
are
for
60
cycle
relays
:
All
OHM
Unit
:
No
.
1
Tap
Setting
(
%
)
2
VA
=
a
+
jb
Input
Tap
Setting
(
%
)
MHO
Unit
:
E
2
Tap
Setting
(
%
)
2
+
(
e
+
jf
)
VA
=
c
+
jd
Input Tap
Setting
(
%
)
The
terms
(
a
+
jb
)
and
(
c
+
jd
)
represent
the burdens
of
the
OHM
and
MHO
unit
restraint
circuits
with
input
and
output taps
on
100
%
.
The
term
(
e
+
jf
)
represents
the
burden
of
the
MHO
unit
polarizing
circuit
.
The values
of
these
terms
are
given
in
Table
VII
.
TABLE
VIIA
POTENTIAL
BURDENS
60
Cycles
Frequency
Rating
(
a
+
jb
)
MHO
Restraint
(
c
+
jd
)
MHO
Polarizing
(
e
+
jf
)
UHM
12.3
+
jO
4.6
-
j
5.7
10.0
+
jO
TABLE
VIIB
BURDENS
FOR
THE
OVERCURRENT
UNIT
VA
at
5
Amps
/
60
Cyc
5
Amps
/
60
Cyc
W
at
Calibration
Range
Rated
Amps
12
.
/
3.56
r
-
4
1
11.5
2
-
8
6
0.8
2.65
4
-
16
12
These burdens
are
measured
with
the
armature
in
the
dropped
-
out
position
.
Values
are
for
minimum
pickup
settings
.
11
Courtesy of NationalSwitchgear.com

GEI
-
98328
Complete
potential
burden
data
with
No
.
1
taps
and
E
2
taps
on
100
%
and
with
the
input
tap
on
100
%
are
given
in
Table
VIII
:
TABLE VIII
MAXIMUM
POTENTIAL
BURDENS
IMPEDANCE
P
.
F
.
WATTS
FREQ
.
VOLTS
V A
HI
OHM
120
ITby
+
jO
1245
+
jl
540
1460
+
jO
515
+
j
109
170
1273
1273
120
0.66
4.6
7.3
MHO
Restraint
MHO
Polarizing
Total
Relay
60
60
120
1.0 10.0
10.0
120
60
0.98 26.8 29.6
The
DC
potential
burden
of
the
OX
transfer
relay
circuit
is
given
in
Table
IX
for
the
3
DC
voltage
taps
:
TABLE IX
VOLTS OHMS
40
000
125
2000
4000
250
CALCULATION
OF
SETTINGS
Table
X
illustrates
qualitatively
how
to
set
the
three
zones
of
the
relays
when
they
are
applied
in
straight
distance
schemes
,
applications
,
see
GEK
-
7384
.
For
directional
comparison
TABLE
X
SETTINGS
ON TWO
TERMINAL
LINES
UNIT
SETTINGS
ON
THREE TERMINAL
LINES
Set for
90
%
of
the
reactance
to
the
nearest
remote
terminal
.
Do
not
include
the
effects
of
infeed
.
or
Set for
90
%
of
the
total
line
.
With
all
three terminal
breakers
closed
,
calculate
the
effective
reactance
seen
by
this
unit
for
a
three
-
phase
fault
at
one
of
the
remote
terminals
.
Repeat
for
a
fault
at
the
second
remote
terminal
.
Include
the
effects
of
infeed
in
both
cases
.
Select
the
larger
of
the
two
reactances
and
set
this
unit
for
at
least
110
%
of
this
reactance
.
02
Set
for
at
least
110
%
of
the
total
line
reactance
.
Since
the
MHO
unit
supervises
first
-
and
second
-
zone
tripping
,
it
must
be
set to
reach
at
least
as
far
as
the
second
-
zone
reactance
unit
.
Actually
the
reach
setting
should be
long
enough
to
provide ample
arc
resistance
accommodation
at
the
balance
point
of
the second
zone
.
Any
additional
reach
would
only
provide
for
additional
back
-
up
protection
for
faults
on
remote
lines
.
M
12
Courtesy of NationalSwitchgear.com

GEI
-
98328
Assume
that
it
is
desired
to
use
GCX
51
B
relays
to
protect
the
two
-
terminal
,
5
mile
,
69
KV
transmission
line
shown
in
Figure
9
.
Maximum
load
current
=
450
amps
CT
Ratio
-
600
/
5
PT
Ratio
-
69
,
000
/
115
Zsec
=
Zprim
X
CT
Ratio
PI
Ratio
120
=
Zsec
=
5
(
0.14
+
j
0.80
)
Z
80
°
0.14
+
j
0.80
ohms
50
U
Zsec
=
0.813
Select
the
standard
-
reach
relay
.
From
a
system
fault
study
,
determine
the
minimum
secondary
fault
current
at
breaker
#
1
for
a
three
-
phase
fault
at
bus
B
.
Now
determine
the
minimum
secondary
fault
current
at
breaker
#
2
for
a
three
-
phase
fault
at
bus
A
.
Both
these
values
should
exceed
5
amperes
for
the
relay
selected
above
,
when
set
on
the
0.5
ohm
base
reach
tap
that
is
determined
below
.
The
percent
tap
setting
for
the
first
-
zone
reactance
unit
is
obtained
from
the
following
equation
:
(
Xmin
)
x
100
T
=
XL
where
:
T
=
#
1
tap
setting
in
percent
Xmin
=
Basic
reach
tap
setting
of
reactance
unit
X
[
_
=
Desired
reactance
reach
in
secondary
phase
-
to
-
neutral
ohms
If
we
assume
that
it
is
desired
to
set
the
first
zone
for
90
%
of
the
distance
to
the
remote
terminal
,
then
:
X
|
_
=
0.9
(
0.80
)
=
0.72
Secondary
ohms
For
this
ohmic
reach
use
a
0.5
ohm
basic
reach
tap
setting
.
Thus
,
Xmin
=
0.50
and
T
=
0
^
50
.
x
100
=
69
<
4
%
Since
the
69.4
%
calculated
from
the
equation
above
is
not
an
integral
number
,
use
the
next
highest
#
1
tap
,
which
is
70
%
.
To
achieve
this
setting
the
tap
lead
from
the
lower
No
.
1
position
would
be
connected
to
the
70
%
point
and
the
tap
lead
from
the
upper
No
.
1
position
would
be
connected
to
the
0
%
point
.
The
second
-
zone
must
be
set
to
reach
beyond
the
far
terminal
.
Assume
that
after
due
consideration
it
is
desired
to
set
the
second
-
zone
reactance
reach
for
1.5
secondary
ohms
.
13
Courtesy of NationalSwitchgear.com

GEI
-
98328
The
percent tap
setting
required
to
obtain
this
reach
is obtained
from the
same
equation
that
was
used
for the
first
zone
.
Since
the
same
unit is
used
for second
-
zone
as
is
used for
first
zone
,
the
same
base
reach
tap
setting
is
common
to
both
zones
.
Thus
,
for the second
-
zone
0.50
x
100
=
33
%
T
=
1.50
To
achieve
this
setting
,
the lower
No
.
2
tap
lead
would
be connected
to
the
30
%
point
,
and
the
upper
No
.
2
tap
lead
would
be connected
to
the
3
%
point
.
The
tap
setting
for
the
third
-
zone
MHO
unit is
given
by
the
following
equation
:
T
=
Zmin
x
100
cos
(
60
-
0
)
ZL
where
:
Third
zone
(
E
2
)
tap
setting
in
percent
.
Minimum
reach of the
MHO
unit
as
marked
on
the
nameplate
,
standard
reach
relay
,
this is
2.5
ohms
.
Desired
impedance
reach
in
secondary
phase
-
to
-
neutral ohms
.
Impedance
of
angle
of
Z
|
_
Angle
of
maximum
torque
of the
MHO
unit
.
T
For
the
Zmin
-
ZL
0
60
°
Assume
that
in
this
case
it
is
desired
to set
the
third
zone
to
reach
2.75
80
°
secondary
phase
-
to
-
neutral
ohms
.
The
percent
tap
setting
for
such
a
reach
is
:
2.5
x
100
cos
(
60
-
80
)
=
85.5
%
Set
the
thircTzone
(
E
?
)
taps
for
86
%
.
Note
that
the
restraint
tap
setting
of the
MHO
unit
must
not
be
set
for
less
than
25
%
.
Also refer
to
Appendix
I
for
possible
further
limitations
on
the
MHO
unit
reach
setting
.
The
instantaneous
unit
setting
should
be
no
lower than
115
%
of
full
-
load
current
.
In
this
case
,
with
600
/
5
CT
'
s
and
a
maximum
load
current
of
450
amperes
,
the
instantaneous
overcurrent
unit
must
be
set to
pick
up
above
:
T
=
2.75
450
x
5
*
1.15
=
4.3
amperes
It
should
be
noted
that
with
such
a
setting
the
GCX
relays
will
not
operate
for
any
faults
that
do
not
produce
at
least
4.3
amperes
.
600
CONSTRUCTION
The
Type
GCX
51
relays
are
assembled
in
the
standard
large
-
size
,
double
-
end
(
L
2
)
drawout
case
,
having
studs
at
both ends
in
the
rear
for
external
connections
.
The
electrical
connections
between
the
relay
units
and the
case
studs
are
made
through
stationary
molded
inner
and
outer
blocks
,
between
which
nests
a
removable
connecting
plug
that
completes
the
circuits
.
The
outer
blocks
attached
to
the
case
have
the
studs
for the
external
connections
,
and
the
inner
blocks
have
the
terminals
for
the
internal
connections
.
14
Courtesy of NationalSwitchgear.com

GEI
-
98328
The
relay
mechanism
is
mounted
in
a
steel
framework
called
a
cradle
,
and
is
a
complete
unit
with
all
leads
being
terminated
at
the
inner
block
.
This
cradle
is
held
firmly
in
the
case
with
a
latch
at
both
top
and
bottom
and
by
a
guide
pin
at
the
back
of
the
case
,
connections
between
the
respective
blocks
of
the
cradle
and
case
,
also
locks
the
latch
in
place
.
The
cover
,
which
is
drawn
to
the
case
by
thumbscrews
,
holds
the
connecting
plugs
in
place
.
A
separate
testing
plug
can
be
inserted
in
place
of
the
connecting
plug
to
test
the
relay
in
place
on
the
panel
,
either
from
its
own
source
of
current
and
voltage
,
or
from
other
sources
.
Or
the
relay
can
be
drawn
out
and
replaced
by
another
that
has
been
tested
in
the
laboratory
.
The
connecting
plug
,
besides
making
the
electrical
The
relay
is
composed
of
three
major
sub
-
assembly
elements
:
1
.
The
bottom
element
includes
the
MHO
or
starting
unit
and
associated
circuit
components
.
This
unit
is
directional
and
detects
the
presence
of
faults
within
the
zone
covered
by
the
relay
.
It
also
initiates
operation
of
the
zone
timer
for
faults
within
its
reach
.
The
middle
element
includes
the
OHM
or
reactance
unit
and
associated
circuit
components
,
measurement
.
2
.
This
unit
provides
accurate
first
-
or
second
-
zone
distance
The
top
element
includes
the
OHM
unit
transfer
auxiliary
(
OX
)
,
the
combination
target
and
seal
-
in
unit
,
the
transactor
associated
with
the
OHM
unit
potential
circuit
,
the
tapped
autotransformer
that
determines
the
reach
of
the
OHM
and
MHO
units
,
and
in
the
case
of
the
type
GCX
51
B
relay
,
the
instantaneous
overcurrent
unit
.
The
tap
block
associated
with
the
autotransformer
is
mounted
along
the
right
side
of
the
relay
.
Figures
1
and
2
show
the
relay
removed
from
its
drawout
case
with
all
major
components
identified
.
Symbols
used
to
identify
circuit
components
are
the
same
as
those
that
appear
on
the
internal
connection
diagram
in
Figure
8
.
3
.
ACCEPTANCE
TESTS
Immediately
upon
receipt
of
the
relay
an
INSPECTION
and
ACCEPTANCE
TEST
should
be
made
to
make
sure
that
no
damage
has
been
sustained
in
shipment
and
that
the
relay
calibrations
have
not
been
disturbed
.
that
readjustment
is
necessary
,
refer
to
the
section
on
SERVICING
.
If
the
examination
or
test
indicates
Visual
Inspection
Check
the
nameplate
stamping
to
make
sure
that
the
model
number
and
rating
of
the
relay
agree
with
the
requisition
.
Remove
the
relay
from
its
case
and
check
that
there
are
no
broken
or
cracked
molded
parts
or
other
signs
of
physical
damage
,
and
that
all
screws
are
tight
.
15
Courtesy of NationalSwitchgear.com

GEI
-
98328
Mechanical
Inspection
It
is
recommended
that the
following
mechanical
adjustments
be
checked
:
1
.
MHO
UNIT
5
-
8
mils
OHM
UNIT
CHECK
POINTS
b
-
8
mi
Is
Kotating
shaft
end
play
120
-
130
mils
35
-
45
mils
Contact
gap
3
-
5
mils
3
-
5
mils
Contact
wipe
There
should be
no
noticeable
friction
in
the
rotating
structure
of
the
OHM
and
MHO
units
.
2
.
Make
sure
control
springs
are
not
deformed
and
spring
convolutions
do
not
touch
each
other
.
3
.
With
the
relay
well leveled
in
its
upright
position
,
the
OHM
unit
and
MHO
unit
contacts
must
be
open
.
The
moving
contacts
of the
OHM
and
MHO
units
should
rest
against
their
backstops
.
The
armature
and
contacts
of the
seal
-
in
unit
should
move
freely
when
operated
by
hand
.
There should
be
at
least
1
/
32
"
wipe
on
the
seal
-
in
contacts
.
4
.
5
.
Make
sure
the
armature
of the
telephone
-
type
relay
(
OX
)
is
moving
freely
.
Check
the
location
of the
contact
brushes
on
the cradle
and
case
blocks
against
the
internal
connection
diagram
for
the
relay
.
6
.
7
.
Electrical
Checks
Before
any
electrical
checks
are
made
on
the
OHM
and
MHO
units
,
the
relay
should
be connected
as
shown
in
Figure
10
and be
allowed
to
warm
up
for
approximately
15
minutes
with
the
potential
circuit
alone
(
studs
17
-
18
)
energized
at
rated
voltage
and
with
the
E
2
and
No
.
1
taps
set
at
100
%
.
The
units
were
warmed
up
prior
to
factory
adjustment
and
if
rechecked
when
cold
will
tend
to
underreach
by
3
%
or
4
%
.
Accurately
calibrated
meters
are
of
course
essential
.
It
is desirable
to
check
the
factory
settings
and
calibrations
by
means
of
the
tests
described
in
the
following
sections
.
The
OHM
and
MHO
units
were
carefully
adjusted
at
the
factory
and
it
is
not
advisable
to
disturb
these
settings
unless
the
following
checks
indicate
conclusively
that
the
settings
have been
disturbed
.
If
readjustments
are
necessary
,
refer
to
the
section
on
SERVICING
for
the
recommended
procedures
.
MHO
Unit
Checks
a
.
Control
Spring
Adjustment
Connect
the
relay
as
shown
in
Figure
10
and
set
the
E
^
tap
leads
at
100
%
.
The
position
of
the
No
.
1
and
No
.
2
tap
leads does
not
affect
this
test
.
Make
sure
that the
relay
is
level
in
its
upright
position
.
16
Courtesy of NationalSwitchgear.com

GEI
-
98328
With the
current set
at
5
amperes
and
the
voltage
across
studs
17
-
18
oat
120
volts
,
set
the
phase
shifter
so
that the
phase
-
angle
meter
reads
300
°
(
i
.
e
.
current
lags
the
voltage
on
studs
17
-
18
by
60
°
)
.
Now reduce
the
voltage
to
2
volts and the
current
to
about
2
amperes
.
Gradually
increase
the
current
until
the
MHO
unit
contacts
just
close
.
This should
occur
between
4.1
-
4.9
amperes
for
the
2.5
Q
mho
,
and
5.1
-
5.9
amperes
for
the
1.0
Q
mho
.
b
.
Ohmic
Reach
With
the
relay
still connected
as
shown
in
Figure
10
and the
E
2
taps
in
the
100
%
position
,
set
the
voltage
at
the value shown
in
Table
XI
for
the
relay
to
be checked
.
Increase the
current
until
the
MHO
unit
contacts
just
close
.
This
should
occur
within
the
limits
shown
in
Table
XI
:
TABLE XI
Equiv
.
Test
Reach
(
0
-
0
Ohms
)
Pickup
Basic
Min
.
Reach
(
0
-
N
Ohms
)
V
17
-
18
Set
At
Relay
Amps
19.4
-
20.6
7
40
V
Short
Reach
T
14.6
-
15.4
Standard
Reach
275
5
75
V
Note
that
for
the
test
conditions
the
MHO
unit
sees
a
phase
-
to
-
phase
fault
of
twice the basic
minimum reach
.
c
.
Anqle
-
of
-
Maximum
-
Torque
Check
For
the
angle
-
of
-
maximum
-
torque
check
,
the
connections
of
Figure
10
will
still
be used
with
the
E
2
taps
still
at
100
%
,
and the
voltage
set
at
the value
shown
in
Table
XI
for
the
relay
to
be
checked
.
The
pickup
should
then be
checked
with the
current
displaced
30
°
from
the
maximum
torque
position
in
both
the
lead
and
lag
direction
.
Set
the
phase
shifter
so
that
the
phase
-
angle
meter
reads
330
°
.
Note
that
while
the
phase
angle
is
being
set
the
current
should
be
at
5
amperes
and
the
voltage
on
studs
17
-
18
should be
increased
temporarily
to
120
volts
.
With
voltage
again
at
the
value shown
in
Table
XI
,
increase the
current
slowly
until
the
MHO
unit
picks
up
.
The
pickup
current
should
be
22
to
24
amperes
for
the
short
-
reach
relay
and
16.5
to
18.2
amperes
for
the
standard
-
reach
relay
.
Now
reset
the
phase
angle
at
270
°
and
again
check
the
current
required
to
pick
up
the
MHO
unit
.
The
pickup
current
should
fall
within
the
same
limits
given
in
the
previous
paragraph
.
Note that the
two
angles
used
in
the
previous
check
,
i
.
e
.
,
330
°
and
270
°
,
are
read
30
°
away
from
the
angle
of
maximum
torque
.
An
examination
of
the
MHO
unit
impedance
characteristic
in
Figure
5
shows that the
ohmic
reach
of
the
unit
should be the
same
at
both
330
°
and
270
°
and
should
be
0.866
times
the
reach
at
the
angle
of
maximum
torque
.
17
Courtesy of NationalSwitchgear.com

GEI
-
98328
OHM
Unit
Checks
a
.
Control
-
Spring
Adjustment
Be
sure
that the
relay
is
well leveled
in
its
upright
position
,
contact
should
just
touch
its
backstop
.
The
moving
b
.
Ohmic
Reach and
Angle
of
Maximum
Torque
Since
the
OHM
unit is
a
reactance
-
measuring
device
,
its
angle
of
maximum
torque
occurs
at
90
°
,
current
lagging
voltage
.
1
.
To
check
the
ohmic
reach
,
use
the
connections
shown
in
Figure
10
.
Set
the
No
.
1
tap
leads
on
100
%
and
set
the
current
at
10
amperes
.
Set
the
phase
shifter
so
that the
phase
-
angle
meter
reads
270
°
(
i
.
e
.
current
lags voltage
by
90
°
)
.
Now
vary
the
voltage
across
studs
17
-
18
until
the
point
is
found where
the
OHM
unit
contacts
just
close
.
This
pickup
point
will
be
different
for the
standard
-
and
short
-
reach forms of the
relay
,
and
also
will
depend
upon
the
setting
of
the
basic
ohmic
reach
taps
.
Table
XIV
shows the
pickup
voltage
point
for
the
intermediate
range
settings
in
the colum headed
90
°
.
A
±
3
%
variation is
permissible
.
2
.
To
check
the
angle
of
maximum
torque
use
the
same
connections
and
settings
as
in
(
1
)
above
except
now
set
the
phase
shifter
so
that the
phase angle
meter
reads
315
°
(
i
.
e
.
current
lags voltage
by
45
°
)
.
Again
vary
the
voltage
across
studs
17
-
18
until
the
point
is
found where the
OHM
unit
contacts
just
close
.
These
points
are
listed
in
Table
XII
for the standard
-
and
short
-
reach forms
of
the
relay
in
the
column headed
45
°
.
A
+
3
%
variation
is
permissible
.
Note
that the
relays
are
normally
shipped
from
the
factory
with
the
basic
minimum
reach
adjustment
taps
on
the
intermediate
setting
,
that
is
,
0.2
ohms
for the
short
-
reach form
and
0.5
ohms
for the standard
-
reach
form
.
TABLE XII
OHM
UNIT
CHECK POINTS
OPERATING
P
0
INTS
(
V
17
_
18
)
I
LAGS
V
BY
+
Z
-
3
%
BASIC
MIN
REACH
SETTING
NO
.
1
TAP
SET
CURRENT
RELAY
900
450
AT
:
8.4
V
14.1
V
0.2
Ohms
0.5
Ohms
100
%
6
V
Short Reach
Stand
.
Reach
T
5
A
100
%
10
A
10
V
Other
Checks
and
Tests
In
addition
to
the
tests
on
the
OHM
and
MHO
units
,
it is
recommended
that
the
following
general
tests
and checks
be
made
as
a
part
of the
ACCEPTANCE
TEST
routine
.
OHM
-
Unit
Transfer
Relay
(
0
X
1
a
.
The
OHM
-
unit
transfer
relay
,
identified
as
OX
in
Figure
8
,
is
provided
with
a
voltage
-
selection
link
to
adapt
it
for
application
on
48
,
125
or
250
volt
DC
control
.
position
.
that the
OX
unit
picks
up
at
80
%
or
less
of the
nominal
tap
voltage
for
each
link
position
.
The
unit
should
be
checked for
correct
operation
on
each
link
Apply
a
variable
source
of
DC
voltage
across
studs
12
-
13
and
check
18
Courtesy of NationalSwitchgear.com

GEI
-
98328
b
.
Target
/
Seal
-
in
Unit
The
target
/
seal
-
in
unit
has
an
operating
coil
tapped
at
0.6
or
2.0
amperes
.
The
relay
is
shipped
from
the
factory
with
the
tap
screw
in
the
0.6
ampere
position
.
The
operating
point
of
the
seal
-
in
unit
can
be
checked
by
connecting
from
a
DC
source
(
+
)
to
stud
11
of
the
relay
and
from
stud
3
through
an
adjustable
resistor
and
ammeter
back
to
(
-
)
.
Connect
a
jumper
from
stud
15
to
stud
3
also
,
so
that
the
seal
-
in
contact
will
protect
the
MHO
unit
contact
.
Then
close
the
MHO
contact
by
hand
and
increase
the
DC
current
until
the
seal
-
in
unit
operates
.
It
should
pick
up
at
tap
value
or
slightly
lower
.
Do
not
attempt
to
interrupt
the
DC
current
by
means
of
the
MHO
contact
.
Instead
,
open
the
circuit
externally
or
turn
off
the
DC
source
.
If
it
is
necessary
to
change
the
tap
setting
,
say
from
0.6
to
2.0
amps
,
proceed
as
follows
:
Remove
the
tap
screw
from
the
left
-
hand
contact
strip
and
insert
it
in
the
2.0
amp
position
of
the
right
-
hand
contact
strip
.
Then
remove
the
screw
from
the
0.6
amp
tap
and
put
it
in
the
vacant
position
in
the
left
-
hand
plate
.
If
this
procedure
is
followed
the
contact
adjustments
will
not
be
disturbed
.
INSTALLATION
PROCEDURE
Location
The
location
of
the
relay
should
be
clean
and
dry
,
free
from
dust
,
excessive
heat
and
vibration
,
and
should
be
well
lighted
to
facilitate
inspection
and
testing
.
Mounting
The
outline
and
panel
-
The
relay
should
be
mounted
on
a
vertical
surface
,
drilling
dimensions
are
shown
in
Figure
32
.
Connections
The
internal
connections
of
the
GCX
51
A
and
B
relays
are
shown
in
Figure
8
.
An
elementary
diagram
of
typical
external
connections
is
shown
in
Figure
3
.
It
will
be
noted
in
Figure
8
that
as
shipped
from
the
factory
,
internal
jumpers
are
connected
between
cradle
terminals
17
-
19
and
18
-
20
.
If
it
is
desired
to
use
a
separate
polarizing
potential
,
these
internal
jumpers
can
be
removed
.
The
restraint
voltage
would
then
be
connected
to
studs
17
-
19
and
the
polarizing
voltage
to
19
-
20
.
Visual
Inspection
Remove
the
relay
from
its
case
and
check
that
there
are
no
broken
or
cracked
component
parts
and
that
all
screws
are
tight
.
Mechanical
Inspection
Recheck
the
seven
adjustments
mentioned
under
Mechanical
Inspection
in
the
section
on
ACCEPTANCE
TESTS
.
19
Courtesy of NationalSwitchgear.com

GEI
-
98328
Electrical
Check
Tests
on
Induction Units
The
manner
in
which
reach
settings
are
made
for
the
OHM
and
MHO
unit
is
briefly
discussed
in
the
CALCULATION
OF SETTINGS
section
.
Examples
of
calculations
for
typical
settings
are
given
in
that
section
.
It
is
the
purpose
of
the
electrical
tests
in
this
section
to
check
the
OHM
and
MHO
unit
ohmic
pick
up
at
the
settings
that have been made for
a
particular
line
section
.
To
eliminate
the
errors
that
may
result
from
instrument
inaccuracies
,
and
to
permit
testing
the
OHM
and
MHO
units
from
a
single
-
phase
AC
test
source
,
the
test
circuit
shown
in
schematic
form
in
Fig
.
11
is
recommended
.
In
this
figure
Rs
+
jXs
is
the
source
impedance
,
SF
is
the fault
switch
,
and
R
|
_
+
jX
|
_
is
the
impedance
of
the
line
section
for
which
the
relay
is
being
tested
.
The
autotransformer
,
TA
,
which
is
across
the fault
switch
and
line
impedance
,
is
tapped
in
10
%
and
1
%
steps
so
that the
line
impedance
R
|
_
+
jX
|
_
may
be
made
to
appear
to
the
relay
very
nearly
as
the
actual
line
on
which
the
relay
is
to
be
used
.
This
is
necessary
since
it is
not
feasible
to
provide
the
portable
test reactor
X
|
_
and
the
test
resistor
with
enough
taps
so
that
the
combination
may
be
made
to
match
any
line
.
For
convenience
in
field
testing
,
the fault
switch
and
tapped
autotransformer
of
Figure
11
have been
arranged
in
a
portable
test
box
,
Cat
.
No
.
102
L
201
,
which
is
particularly
adapted
for
testing
directional
and
distance
relays
.
The box
is
provided
with
terminals
to
which
the
relay
current
and
potential
circuits
as
well
as
the
line
and
source
impedances
may
be
readily
connected
.
For
a
complete
description
of the
test
box
,
the
user
is
referred
to
GET
-
3474
.
a
.
Testing
the
OHM
Unit
To
check
the
calibration
of the
OHM
unit
,
it
is
suggested
that
the
portable
test
box
,
Cat
.
No
.
102
L
201
;
portable
test reactor
,
Cat
.
6054975
;
and
test
resistor
,
Cat
.
6158546
be
arranged
with
Type
XLA
test
plugs
according
to
Figure
12
.
These
connections
of the
test
box
and other
equipment
are
similar
to
the
schematic
connections
shown
in
Figure
11
except
that
the
Type
XLA
test
plug
connections
are
now
included
.
Use
of
the
source
impedance
Rs
+
jXs
,
simulating
the
conditions
that
would be
encountered
in
practice
,
is
necessary
only
if
the
relay
is
to
be
tested
for
overreach
or
contact
coordination
,
tests
which
are
not
normally
considered
necessary
at
the
time
of
installation
or
during
periodic
testing
,
impedance
will
usually
be
necessary
in
the
source
connection
to
limit
current
in
the fault
circuit
to
a
reasonable
value
,
especially
when
a
short
-
reach
unit
is
to
be
checked
,
and
it is
suggested
that
a
reactor
of
suitable
value
be
used
for
this
purpose
since this
will
tend
to
limit harmonics
in
the
fault
current
.
Since
the
relay
is
to
be
tested
for
the
ohmic
reach that
it
will
have
when
in
service
,
the
value
of
X
|
_
to
select
will
be
the
portable
test
-
reactor
tap
nearest
above
twice
the
relay
phase
-
to
-
neutral
ohmic
reach
.
Explanation
of the
twice
factor
is
as
follows
;
The
relay
as
normally
connected
(
Vl
-
2
potential
and
11
-
12
current
)
measures
positive
-
sequence
phase
-
to
-
neutral
reactance
.
For
a
phase
-
to
-
phase
fault
,
the
fault
current
is
forced
by
thephase
-
to
-
phase
voltage
through
the
impedance
of
each
of the
involved
phases
,
test
circuit
,
the
line
impedance
,
Z
|
_
,
is
in
effect
the
sum
of the
impedance
of
each of
the
phase
conductors and
must
be
so
arranged
in
order
to
be
equivalent
to
the actual fault
condition
.
Since
the
impedance
of
each
phase
must
be used
Some
In
the
20
Courtesy of NationalSwitchgear.com