ABB Relion 650 Series Applications Manual page 252

Section 16
Requirements
=
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 V1 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
> 0.75 · (maximum of E
E
kneeANSI
EQUATION2101 V1 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.
16.2 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.
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.
The transient responses for three different standard transient response classes, T1, T2 and T3 are
specified in chapter 6.503 of the standard. CCVTs according to all classes can be used.
The protection IED has effective filters for these transients, which gives secure and correct
operation with CCVTs.
246
× × + =
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)
max imum of E
alreq
according to IEC 61869-2. Therefore, the CTs according to ANSI/IEEE must
al
kneeANSI
)
alreq
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× × + × ×
R 20 I Z
S N CT S N bANS I
kneeANSI
can approximately be estimated to 75 % of
kneeANSI
that fulfills the following:
1MRK 505 287-UUS B
(Equation 39)
(Equation 40)
that is graphically
kneeANSI
normally has a lower value than
(Equation 41)
Busbar protection REB650
Application manual
M11608-3 v5