Current Transformers According To Ansi/Ieee; Voltage Transformer Requirements - Hitachi Relion 670 Series Applications Manual

1MRK511407-UUS Rev. N
Therefore, the CTs according to class PX, PXR, X and TPS must have a rated knee point e.m.f. E
that fulfills the following:
= ×
S TD S
EQUATION1893.ANSI V1 EN-US
23.1.7.3

Current transformers according to ANSI/IEEE

Current transformers according to ANSI/IEEE are partly specified in different ways. A rated secondary
terminal voltage V
deliver to a standard burden at 20 times rated secondary current without exceeding 10 % ratio correction.
There are a number of standardized V
corresponding rated equivalent limiting secondary e.m.f. E
=
E
a lANS I
EQUATION1682 V1 EN-US
where:
Z The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class (W)
bANSI
V The secondary terminal voltage for the specific C class (V)
ANSI
The CTs according to class C must have a calculated rated equivalent limiting secondary e.m.f. E
that fulfils the following:
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
knee-point e.m.f. according to IEC and BS. V
corresponding E
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.
23.2

Voltage transformer requirements

The performance of a protection function will depend on the quality of the measured input signal.
Transients caused by capacitive Coupled voltage transformers (CCVTs) can affect some protection
functions.
Magnetic or capacitive voltage transformers can be used.
Phasor measurement unit RES670
Application manual
+ - ×
(1 TD S )
Old Calculated
is specified for a CT of class C. V
ANSI
× × + =
20 I R V 20 I
S N CT ANS I
>
maximum of E
alreq
according to IEC 61869-2. Therefore, the CTs according to ANSI/IEEE must have a
al
that fulfills the following:
kneeANSI
> ×
0.75 (max imum of E
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is the secondary terminal voltage the CT will
ANSI
values for example, V
ANSI
alANSI
× × + × ×
R 20 I Z
S N CT S N bANS I
kneeANSI
can approximately be estimated to 75 % of the
kneeANSI
)
alreq
is 400 V for a C400 CT. A
ANSI
can be estimated as follows:
that is graphically
kneeANSI
normally has a lower value than the
Section 23
Requirements
knee
(Equation 106)
M11623-22 v6
(Equation 107)
alANSI
(Equation 108)
(Equation 109)
M11608-3 v5
335