GE STD16C - CONSTRUCTION AND COMPONENTS

GEK—45307
CONSTRUCTION
Figure
6
shows
the
internal
arrangement
of
the
components
of
the
STD15C
relay.
Refer
also to
the
internal
connection
diagrams,
Figures
10
and 11,
which
will
identify
the
parts
more
completely.
CURRENT
TRANSFORMERS
In
the
Type
STD15C
relay,
the
through-current
transformer
has
two
primary
windings,
one
for
each
line-current-transformer
circuit.
Winding
No.
1
terminates
at
stud 6
and
winding
No.
2
terminates
at
stud
4.
In
the
Type STD16C
relay,
there
are
three
separate
through—current
transformers,
each
with
only one
primary
winding,
and
each
terminating
at a
separate
stud,
windings
No.
I,
No.
2
and
No.
3
corresponding
to
studs
6,
4 and 3
in
that
order.
In
both
relays
there
is
a
differential—current
transformer
with
one
primary
lead
brought
out
to
stud 5.
The
primary
circuit
of
each of
these
transformers
is
completed
through
a
special
tap
block
arrangement.
Two
or
three
horizontal
rows
of
tap
positions
are
provided
(depending
on
whether
the
relay
is
a
Type
STD15C
or
STD16C),
one
row
for
each
through-current
transformer
winding. A
tap
on
the differential—current
transformer
is
connected
to
a
corresponding
tap of
the
through—current
restraint
windings
by
inserting
tap
plugs
in
the
tap blocks.
When the
STD16C
relay
is
used
on
four-circuit
applications,
as
shown
in
Figure
1,
the
fourth
circuit
CT
is
connected
to
stud
7,
and
the
jumper
normally
connected
between
terminals 6
and
7
at
the
rear of
the
relay
cradle
should
be
disconnected
at
the
terminal 6
end
and reconnected
to
the
upper
row
in
the tap
block
(above
the row
marked
winding
1),
which
connects
it
directly
to
the
differential-current
transformer
in
the
STD
relay.
The
terminal
on
the
movable
lead
should be
placed
under the
tap
screw
that
gives
the
best
current
match for
the
current
in
the
movable
lead.
The
taps
permit
matching
of
unequal
line—current
transformer
secondary
currents.
The
tap
connections
are so
arranged
that
in
matching
the secondary
currents,
when a
tap
plug
is
moved
from
one
position
to
another
in
a
horizontal
row,
corresponding
taps
on
both
the differential—current
transformer
winding
and
one
of
the
through—
current
transformer
windings
are
simultaneously
selected
so
that
the
percent
through-current
restraint
remains
constant.
It
should
be
recognized
that
pickup
current
flows
not
only
through
differential-
current
transformer
but
also
through
one
of
the
primary
windings
of
the
through-
current
transformer,
producing
some
restraint.
However,
compared
to
the
operating
energy,
this
quantity
of
restraint
is
so
small
that
it
may
be
assumed
to
be
zero.
THROUGH-CURRENT
RESTRAINT
CIRCUIT
A
full
wave
bridge
rectifier
receives
the
output
of
the
secondary
of
each
through
current
restraint
transformer.
In
the
STD16C
relay,
the
DC
outputs
of
all
three
units
are
connected
in
parallel.
The
total output
is
directed
to
the
percent
slope
14