GE STD16C - OPERATION AND MAINTENANCE; OPERATION; MAINTENANCE

GEK-45307
This
curve
represents
the 510
relay
characteristic.
Measurement
of
a
voltage
across
studs
8
and
9
which
is
75%
or less
of the
value
given
on
the curve,
does not
necessarily
indicate
that
the
relay
will
operate
at
higher
through-current
values.
This
is
especially
true
where
very
high
through-faults may
cause
saturation.
Small
rectifier-type
AC voltmeters
are
suitable
for
the
measurement
of
unbalance.
The
voltmeter should
not be
left
permanently
connected,
since
the shunt
current
it
draws
reduces
the
relay
sensitivity.
PERCENT
SLOPE
SETTING
Scribe
marks
for
15,
25
and
40%
slope
settings
are
provided
in both
the
STD15
and
STD16
relays.
It
is
common
practice
to use
the
25%
setting
unless
special
connections
make
it
advisable
to
use
one
of
the others.
See
the
corresponding
heading
under
CALCULATIONS
for further
details.
OPERAT
ION
TARGETS
Targets
are
provided
for
both
the
seal-in
unit
and
the
instantaneous
overcurrent
unit.
In
the event
of
an internal
fault,
one
or
both
of
these
units
will
operate,
depending
upon
the
fault
magnitude.
This
will
produce
a
target
indication
of
the
particular
unit
which
operates.
After
a
fault
is cleared,
the
target
should
be
reset
by the
reset
slide
located
at the
lower
left—hand
corner
of
the
relay.
DISABLING
OF
TYPE
STD
RELAY
CAUTION
When
bypassing
a breaker
for
maintenance,
it
will
be necessary
to
disable
[_
the
relay
to prevent
false
tripping.
If the
disabling
of
the relay
is
done
by
a
remote
switch,
rather
than
by
removing
the
relay
connection
plug,
the following
precautions
should
be
taken:
1.
The
relay
must
be disabled
by short-circuiting
studs
8
and
9
of
the
relay,
or
by opening
the
trip
circuit
at stud
1.
2.
If
the
CT
secondaries are short-circuited
as
part
of
the
disabling
procedure,
the trip
circuit
should
be
opened
at
stud
1,
and
studs
8
and
9
should
be short-
circuited
first.
It
is
not
sufficient
to rely
on
short
circuiting
the
CT
secondaries
alone,
because
any difference
in time
of
shorting
them
may
cause
false
tripping.
MAT
NTENANCE
CONTACT
CLEANING
For
cleaning
fine silver
contacts,
a
flexible
burnishing
tool
should
be
used.
This
consists
of
a flexible
strip
of
metal
with
an
etched-roughened
surface,
resembling
23