ABB RELION 670 Series Applications Manual page 434

Section 20
Requirements
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.
20.2 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.
20.3 SNTP server requirements
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 least equipped with a
real-time operating system, that is not a PC with SNTP server software. The SNTP server should be
stable, that is, either synchronized from a stable source like GPS, or local without synchronization.
Using a local SNTP server without synchronization as primary or secondary server in a redundant
configuration is not recommended.
428
>
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
kneeANSI
can approximately be estimated to 75 % of
kneeANSI
that fulfills the following:
)
alreq
1MRK 505 337-UUS A
(Equation 105)
that is graphically
kneeANSI
normally has a lower value than
(Equation 106)
GUID-588FCD12-C494-445E-8488-8287B34EFD9A v4
Application manual
M11608-3 v5