Rated Equivalent Secondary E.m.f. Requirements; Current Transformer Requirements For Cts According To Other Standards; Current Transformers According To Iec 61869-2, Class P, Pr; Current Transformers According To Iec 61869-2, Class Px, Pxr (And Old Iec 60044-6, Class Tps And Old British Standard, Class X) - Hitachi Relion 670 Series Applications Manual

Section 23
Requirements
minimum operating value for all faults that are to be detected with the selected CT ratio. It should also be
verified that the maximum possible fault current is within the limits of the IED.
The current error of the current transformer can limit the possibility to use a very sensitive setting of a
sensitive residual overcurrent protection. If a very sensitive setting of this function will be used it is
recommended that the current transformer should have an accuracy class which have an current error at
rated primary current that is less than ±1% (for example, 5P). If current transformers with less accuracy
are used it is advisable to check the actual unwanted residual current during the commissioning.
23.1.6

Rated equivalent secondary e.m.f. requirements

With regard to saturation of the current transformer all current transformers of high remanence and low
remanence type that fulfill the requirements on the rated equivalent limiting secondary e.m.f. E
can be used. The characteristic of the non remanence type CT (TPZ) is not well defined as far as the
phase angle error is concerned. If no explicit recommendation is given for a specific function we therefore
recommend contacting Hitachi Energy to confirm that the non remanence type can be used.
The CT requirements for the different functions below are specified as a rated equivalent limiting
secondary e.m.f. E
other classes and standards are given at the end of this section.
23.1.7 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
al
applications it is possible to approximately calculate a secondary e.m.f. of the CT comparable with E
By comparing this with the required rated equivalent limiting secondary e.m.f. E
if the CT fulfills the requirements. The requirements according to some other standards are specified
below.
23.1.7.1

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
is approximately equal to the corresponding E
have a secondary limiting e.m.f. E
E
ALF
EQUATION1383 V4 EN-US
23.1.7.2 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 (E
knee k
value of the E
a general relation between the E
334
according to the IEC 61869-2 standard. Requirements for CTs specified according to
al
according to the IEC 61869-2 standard. From different standards and available data for relaying
ALF

max E
alreq
for class PX and PXR, E
kneeBS
is lower than the corresponding E
knee
knee
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. Therefore, the CTs according to class P and PR must
al
that fulfills the following:
for class X and the limiting secondary voltage V
according to IEC 61869-2. It is not possible to give
al
and the E but normally the E
al
1MRK511407-UUS Rev. N
it is possible to judge
alreq
. The value of the E
ALF
for TPS). The
al
is approximately 80 % of the E
knee
Phasor measurement unit RES670
Application manual
SEMOD53723-1 v1
M11616-3 v4
below
al
SEMOD53771-1 v1
M11623-4 v3
.
al
M11623-6 v4
ALF
(Equation 105)
M11623-14 v5
.
al