A CT according to ANSI/IEEE is also specified by the knee point voltage
U
kneeANSI
that is graphically defined from an excitation curve. The knee point
voltage U
kneeANSI
normally has a lower value than the knee-point e.m.f. according
to IEC and BS. U
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 U
kneeANSI
that fulfills the following:
kneeANSI alreq
V 0.75 (max imum of E )> ×
EQUATION2101 V2 EN-US (Equation 546)
25.2 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 voltage transformers
(CVTs) can affect some protection functions.
Magnetic or capacitive voltage transformers can be used.
The capacitive voltage transformers (CVTs) should fulfill the requirements
according to the IEC 61869-5 standard regarding ferro-resonance and transients.
The ferro-resonance requirements of the CVTs 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. CVTs according to all
classes can be used.
The protection IED has effective filters for these transients, which gives secure and
correct operation with CVTs.
25.3 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 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.
Section 25 1MRK 506 369-UEN B
Requirements
886 Line distance protection REL670 2.2 IEC
Application manual
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