ABB Relion REC670, Applications Manual

Page: 641 / 658

24.1.7 Current transformer requirements for CTs according to other
standards
SEMOD53771-1 v1
M11623-4 v3
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
al
according to the IEC 61869-2 standard. From
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
al
. By
comparing this with the required rated equivalent limiting secondary e.m.f. E
alreq
it is
possible to judge if the CT fulfills the requirements. The requirements according to
some other standards are specified below.
24.1.7.1 Current transformers according to IEC 61869-2, class P, PR
M11623-6 v4
A CT according to IEC 61869-2 is specified by the secondary limiting e.m.f. E
ALF
. The
value of the E
ALF
is approximately equal to the corresponding E
al
. Therefore, the CTs
according to class P and PR must have a secondary limiting e.m.f. E
ALF
that fulfills the
following:
ALF alreq
E max E

EQUATION1383 V4 EN-US
(Equation 133)
24.1.7.2 Current transformers according to IEC 61869-2, class PX, PXR (and old
IEC 60044-6, class TPS and old British Standard, class X)
M11623-14 v5
CTs according to these classes are specified approximately in the same way by a rated
knee point e.m.f. E
knee
(E
k
for class PX and PXR, E
kneeBS
for class X and the limiting
secondary voltage V
al
for TPS). The value of the E
knee
is lower than the corresponding
E
al
according to IEC 61869-2. It is not possible to give a general relation between the
E
knee
and the E
al
but normally the E
knee
is approximately 80 % of the E
al
. Therefore,
the CTs according to class PX, PXR, X and TPS must have a rated knee point e.m.f.
E
knee
that fulfills the following:
(1 )
= × + - ×
Old Calculated
S TD S TD S
EQUATION1893.ANSI V1 EN-US
(Equation 134)
1MRK 511 401-UUS A
Section 24
Requirements
Bay control REC670 2.2 ANSI 635
Application manual