GE STD16C - RATINGS AND CHARACTERISTICS

GEK-45307
hA
Repeat - Percent Ratio
Error
1.
Burden
on
CTs
Line
A,
Z
=
0.192
+
0.205
+ 0.568
= 0.965
Line
B,
Z
0.156
+
0.188
+
0.568
=
0.912
Line
C,
7
= 0.096
+
0.226
+
0.568
= 0.890
2.
Impedance
Ohms
0.965
0.912
0.890
3.
8
times
Tap,
Amperes
36.8
25.6
69.6
4.
CT voltage
required
(17)
35.6
23.4
61.9
5.
‘C
required, from
excitation
curve
1.1
0.25
0.17
5.
%
of
Ratio
Error
3.1%
1.0%
0.3%
Percent
error
is
less
than
20%,
so
CT
taps
and
relay
taps
are
satisfactory.
III
Percent
Slope
Setting
1.
Assume
load
ratio
control
maximum
range
10.0%
2.
Relay
tap
mismatch,
from
IA above (Lines
A-B)
4.6%
Use
25%
setting
14.6%
RATI
NGS
MODELS
12STD15C AND
12STD16C
Continuous
Rating
The
through-current
transformer
and
differential-current
transformer
will
stand
twice
tap
value
for
any
combination
of
taps,
or
they
will
stand
twice
tap
value
if
all
but
one
of
the
restraint
windings
carry 0 current,
and
the
full restraint
current
(equal
to
twice
tap
value)
flows
through
the
differential—current
transformer.
Short
Time
Rating
(Thermal)
220
amperes
for
1
second,
measured
in
the
primary
of
any
transformer
of
the
type
STD
relay.
Higher
currents
may
be
applied
for
shorter
lengths
of
time
in
accordance
with
the
following
equation:
= 48,400
where
=
current
amperes
t
=
time
in
seconds.
Short
Time
(Electrical
For
both
the
STD15C
and
STD16C the
sum
of
the
multiples
of
tap
current fed
to
the
relay
from
the
several
sets
of
current
transformers
should
not
exceed
150.
These
multiples
should
be
calculated
on the
basis
of
RMS
symmetrical
fault
current.
This
limitation
is
a
result
of
the
voltage
rating
of
the
rectifiers
in
the
through—
current
restraint
circuit.
Note
that
in
Figure
1
external
fault
current
can
flow
through
circuit
breakers
52—1
and
52—2
without
being
limited
by
the
transformer
i
in
peda
n
ce.