23.1.7.1
Current transformers according to IEC 61869-2, class P, PR
M11623-6 v3
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:
2 max
alreq
E
max E
>
EQUATION1383 V3 EN-US
(Equation 574)
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)
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
U
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:
(
)
knee
k
kneeBS
al
alreq
E
E
E
U
0.8 maximum of E
»
»
»
>
×
EQUATION2100 V2 EN-US
(Equation 575)
23.1.7.3
Current transformers according to ANSI/IEEE
M11623-22 v6
Current transformers according to ANSI/IEEE are partly specified in different ways. A rated
secondary terminal voltage U
ANSI
is specified for a CT of class C. U
ANSI
is the secondary
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
ANSI
values for
example, U
ANSI
is 400 V for a C400 CT. A corresponding rated equivalent limiting secondary
e.m.f. E
alANSI
can be estimated as follows:
alANSI
sr
ct
ANSI
sr
ct
sr
bANSI
E
20 I
R
U
20 I
R
20 I
Z
=
×
×
+
=
×
×
+
×
×
EQUATION971 V2 EN-US
(Equation 576)
where:
Z
bANSI
The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class
(
W
)
U
ANSI
The secondary terminal voltage for the specific C class (V)
The CTs according to class C must have a calculated rated equivalent limiting secondary e.m.f.
E
alANSI
that fulfils the following:
alANSI
alreq
E
maximum of E
>
EQUATION1384 V2 EN-US
(Equation 577)
1MRK 505 343-UEN B
Section 23
Requirements
741
Application manual
Summary of Contents for Relion 670 series
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