GE GCX51A - Electrical Check; Testing the OHM Unit; Tests

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
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