EQUATION1383 V2 EN (Equation 11)
2.1.7.2 Current transformers according to IEC 60044-1, class PX, 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
(E
k
for class PX, 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 60044-6. 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, 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 (Equation 12)
2.1.7.3 Current transformers according to ANSI/IEEE
Current transformers according to ANSI/IEEE are partly specified in different ways. A
rated secondary terminal voltage V
ANSI
is specified for a CT of class C. V
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, V
ANSI
is 400 V for a C400 CT. A
corresponding rated equivalent limiting secondary e.m.f. E
alANSI
can be estimated as
follows:
a lANS I
SN CT ANS I S N CT S N bANSI
E 20 I R V 20 I R 20 I Z= × × + = × × + × ×
EQUATION1682 V1 EN
(Equation 13)
where:
Z
bANSI
The impedance (that is, complex quantity) of the standard ANSI burden for the specific C class (W)
V
ANSI
The secondary terminal voltage for the specific C class (V)
Section 2 1MRK504116-UUS C
Requirements
28
Application manual
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