Voltage Transformer Requirements - ABB REB670 Applications Manual

Section 19
Requirements
19.2
19.3
488
normally has a lower value than the knee-point e.m.f. according to IEC and BS. V
can approximately be estimated to 75 % of the corresponding E
61869-2. Therefore, the CTs according to ANSI/IEEE must have a knee point voltage
V that fulfills the following:
kneeANSI
> ×
V 0.75 (max imum of E
kneeANSI
EQUATION2101 V2 EN
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.

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.
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.
)
alreq
1MRK 505 337-UUS -
kneeANSI
according to IEC
al
(Equation 99)
Application manual