ABB RELION 670 Series Applications Manual page 433

1MRK 505 337-UUS A
secondary e.m.f. E
data for relaying applications it is possible to approximately calculate a secondary e.m.f. of the CT
comparable with E
e.m.f. E
alreq
some other standards are specified below.
20.1.7.1 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
must have a secondary limiting e.m.f. E
E
2 max
EQUATION1383 V3 EN-US
20.1.7.2 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
knee
TPS). The value of the E
possible to give a general relation between the E
approximately 80 % of the E
a rated knee point e.m.f. E
= ×
S TD S
EQUATION1893.ANSI V1 EN-US
20.1.7.3 Current transformers according to ANSI/IEEE
Current transformers according to ANSI/IEEE are partly specified in different ways. A rated
secondary terminal voltage V
voltage the CT will deliver to a standard burden at 20 times rated secondary current without
exceeding 10 % ratio correction. There are a number of standardized V
V is 400 V for a C400 CT. A corresponding rated equivalent limiting secondary e.m.f. E
ANSI
be estimated as follows:
=
E
a lANS I
EQUATION1682 V1 EN-US
where:
Z
bANSI
V
ANSI
Application manual
according to the IEC 61869-2 standard. From different standards and available
al
. By comparing this with the required rated equivalent limiting secondary
al
it is possible to judge if the CT fulfills the requirements. The requirements according to
>
max E
alreq
(E for class PX and PXR, E
k
is lower than the corresponding E
knee
. Therefore, the CTs according to class PX, PXR, X and TPS must have
al
that fulfills the following:
knee
+ - ×
(1 TD S )
Old Calculated
ANSI
× × + =
20 I R V 20 I
S N CT ANS I
The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class (W)
The secondary terminal voltage for the specific C class (V)
. Therefore, the CTs according to class P and PR
al
that fulfills the following:
alf
for class X and the limiting secondary voltage V
kneeBS
and the E
knee
is specified for a CT of class C. V
× × + × ×
R 20 I Z
S N CT S N bANS I
. The value of the E
alf
according to IEC 61869-2. It is not
al
but normally the E
al knee
is the secondary terminal
ANSI
values for example,
ANSI
Section 20
Requirements
M11623-6 v3
alf
(Equation 102)
M11623-14 v5
for
al
is
(Equation 103)
M11623-22 v6
can
alANSI
(Equation 104)
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