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1MRK 505 370-UEN D
R
ct
R
L
S
R
Independent of the value of I
following:
³
E
E
al
EQUATION1077 V2 EN-US
where
I
kmax
21.1.7
Current transformer requirements for CTs according to other
standards
All kinds of conventional magnetic core CTs are possible to use with the IEDs if they fulfill the
requirements corresponding to the above specified expressed as the rated equivalent limiting
secondary e.m.f. E
available data for relaying applications it is possible to approximately calculate a secondary
e.m.f. of the CT comparable with E
limiting secondary e.m.f. E
requirements according to some other standards are specified below.
21.1.7.1
Current transformers according to IEC 61869-2, class P, PR
A CT according to IEC 61869-2 is specified by the secondary limiting e.m.f. E
the E
ALF
P and PR must have a secondary limiting e.m.f. E
E
ALF
EQUATION1383 V4 EN-US
21.1.7.2
Current transformers according to IEC 61869-2, class PX, PXR (and old
IEC 60044-6, class TPS and old British Standard, class X)
CTs according to these classes are specified approximately in the same way by a rated knee
point e.m.f. E
U
for TPS). The value of the E
al
61869-2. It is not possible to give a general relation between the E
Busbar protection REB670
Application manual
The secondary resistance of the CT (W)
The resistance of the secondary cable and additional load (W). The loop
resistance containing the phase and neutral wires, must be used for faults
in solidly earthed systems. The resistance of a single secondary wire should
be used for faults in high impedance earthed systems.
The burden of an IED current input channel (VA). S
I
=1 A and S
=0.150 VA/channel for I
r
R
the maximum required E
op
æ
I
=
×
×
sr
I
ç
alreq max
k max
I
è
pr
Maximum primary fundamental frequency current for close-in faults (A)
according to the IEC 61869-2 standard. From different standards and
al
it is possible to judge if the CT fulfills the requirements. The
alreq
is approximately equal to the corresponding E
max E
alreq
(E
for class PX and PXR, E
knee
k
knee
=5 A
r
ö
S
+
+
R
R
R
÷
ct
L
2
I
ø
r
. By comparing this with the required rated equivalent
al
al
that fulfills the following:
ALF
for class X and the limiting secondary voltage
kneeBS
is lower than the corresponding E
=0.020 VA/channel for
R
is specified according to the
al
. The value of
ALF
. Therefore, the CTs according to class
according to IEC
al
and the E
knee
Section 21
Requirements
(Equation 98)
SEMOD53771-1 v1
M11623-4 v3
M11623-6 v4
(Equation 99)
M11623-14 v5
but normally
al
455
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