Current Transformer Requirements For Cts According To Other Standards - ABB REC670 Applications Manual

1MRK 511 401-UUS A
24.1.7
24.1.7.1
24.1.7.2
Bay control REC670 2.2 ANSI
Application manual
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
different standards and available data for relaying applications it is possible to
approximately calculate a secondary e.m.f. of the CT comparable with E
comparing this with the required rated equivalent limiting secondary e.m.f. E
possible to judge if the CT fulfills the requirements. The requirements according to
some other standards are specified below.
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
value of the E is approximately equal to the corresponding E
ALF
according to class P and PR must have a secondary limiting e.m.f. E
following:

E max E
ALF alreq
EQUATION1383 V4 EN-US
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 (E
knee
secondary voltage V for TPS). The value of the E
al
E according to IEC 61869-2. It is not possible to give a general relation between the
al
E and the E but normally the E
knee al
the CTs according to class PX, PXR, X and TPS must have a rated knee point e.m.f.
E that fulfills the following:
knee
= × + - ×
S TD S (1 TD S )
Old Calculated
EQUATION1893.ANSI V1 EN-US
according to the IEC 61869-2 standard. From
al
for class PX and PXR, E
k
is approximately 80 % of the E
knee
Section 24
Requirements
. By
al
. Therefore, the CTs
al
that fulfills the
ALF
for class X and the limiting
kneeBS
is lower than the corresponding
knee
. Therefore,
al
SEMOD53771-1 v1
M11623-4 v3
it is
alreq
M11623-6 v4
. The
ALF
(Equation 133)
M11623-14 v5
(Equation 134)
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