alANSI
alreq
E
maximum of E
>
EQUATION1384 V2 EN-US
(Equation 100)
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 CTs 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 101)
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.
21.2
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.
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.
21.3
SNTP server requirements
GUID-588FCD12-C494-445E-8488-8287B34EFD9A v4
The SNTP server to be used is connected to the local network, that is not more than 4-5
switches or routers away from the IED. The SNTP server is dedicated for its task, or at
1MRK 505 370-UUS A
Section 21
Requirements
Busbar protection REB670 2.2 ANSI
533
Application manual
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