ABB Relion 670 Series Applications Manual page 515

1MRK 511 358-UUS A
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
22.1.7.3 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
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
A CT according to ANSI/IEEE is also specified by the knee point voltage V
defined from an excitation curve. The knee point voltage V
the knee-point e.m.f. according to IEC and BS. V
the corresponding E
have a knee point voltage V
V
kneeANSI
EQUATION2101 V2 EN-US
The following guide may also be referred for some more application aspects of ANSI class CTs:
IEEE C37.110 (2007), IEEE Guide for the Application of Current Transformers Used for Protective
Relaying Purposes.
Application manual
. 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)
>
maximum of E
alreq
according to IEC 61869-2. Therefore, the CTs according to ANSI/IEEE must
al
kneeANSI
> ×
0.75 (max imum of E
and the E
knee
is specified for a CT of class C. V
× × + × ×
R 20 I Z
S N CT S N bANS I
can approximately be estimated to 75 % of
kneeANSI
that fulfills the following:
)
alreq
but normally the E
al
is the secondary terminal
ANSI
values for example,
ANSI
that is graphically
kneeANSI
normally has a lower value than
kneeANSI
Section 22
Requirements
is
knee
(Equation 138)
M11623-22 v6
can
alANSI
(Equation 139)
(Equation 140)
(Equation 141)
509