a lANS I SN CT ANSI SN CT S N bANS I
E 20 I R V 20 I R 20 I Z= × × + = × × + × ×
EQUATION1682 V1 EN-US (Equation 307)
where:
Z
bANSI
The impedance (that is, with a 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)
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 308)
A CT according to ANSI/IEEE is also specified by the knee point voltage V
kneeANSI
that is graphically defined from an excitation curve. The knee point voltage V
kneeANSI
normally has a lower value than the knee-point e.m.f. according to IEC and BS.
V
kneeANSI
can approximately be estimated to 75 % of the corresponding E
al
according
to IEC 61869-2. Therefore, the CT
s according to ANSI/IEEE must have a knee point
voltage V
kneeANSI
that fulfills the following:
kneeANSI alreq
V 0.75 (max imum of E )> ×
EQUATION2101 V2 EN-US (Equation 309)
The following guide may also be referred for some more application aspects of ANSI
class CT
s: IEEE C37.1
10 (2007), IEEE Guide for the Application of Current
Transformers Used for Protective Relaying Purposes.
24.2 Voltage transformer requirements
M11608-3 v5
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.
The capacitive voltage transformers (CCVTs) should fulfill the requirements according
to the IEC 61869-5 standard regarding ferro-resonance and transients. The ferro-
resonance requirements of the CCVTs are specified in chapter 6.502 of the standard.
Section 24 1MRK 502 071-UUS A
Requirements
810 Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
Application manual
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