ABB Relion 670 Series Applications Manual page 611

1MRK 511 401-UEN Rev. K
e.m.f. of the CT comparable with E
limiting secondary e.m.f. E
requirements according to some other standards are specified below.
25.1.7.1 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
25.1.7.2 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
the E
knee
TPS must have a rated knee point e.m.f. E
»
E
knee
EQUATION2100 V2 EN-US
25.1.7.3 Current transformers according to ANSI/IEEE
Current transformers according to ANSI/IEEE are partly specified in different ways. A rated
secondary terminal voltage U
terminal 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 U
example, U
e.m.f. E
E
alANSI
EQUATION971 V2 EN-US
where:
Z
bANSI
U
ANSI
The CTs according to class C must have a calculated rated equivalent limiting secondary e.m.f.
E that fulfils the following:
alANSI
E
alANSI
EQUATION1384 V2 EN-US
Bay control REC670
Application manual
alreq
is approximately equal to the corresponding E

max E
alreq
(E for class PX and PXR, E
knee k
knee
is approximately 80 % of the E
(
» » > ×
E E U 0.8 maximum of E
k kneeBS al
ANSI
is 400 V for a C400 CT. A corresponding rated equivalent limiting secondary
ANSI
can be estimated as follows:
alANSI
= × × +
20 I R U
sr ct ANSI
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)
>
maximum of E
alreq
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. By comparing this with the required rated equivalent
al
it is possible to judge if the CT fulfills the requirements. The
that fulfills the following:
ALF
for class X and the limiting secondary voltage
kneeBS
is lower than the corresponding E
. Therefore, the CTs according to class PX, PXR, X and
al
that fulfills the following:
knee
)
alreq
is specified for a CT of class C. U
= × × + ×
20 I R 20 I
sr ct
ALF
. Therefore, the CTs according to class
al
according to IEC
al
and the E
knee
is the secondary
ANSI
×
Z
sr bANSI
Section 25
Requirements
M11623-6 v4
. The value of
(Equation 202)
M11623-14 v5
but normally
al
(Equation 203)
M11623-22 v6
values for
ANSI
(Equation 204)
(Equation 205)
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