Voltage Transformer Requirements - ABB RER670 Applications Manual

Section 22
Requirements
22.2
484
CT. A corresponding rated equivalent limiting secondary e.m.f. E
estimated as follows:
= × × +
E 20 I R
alANSI sr ct
EQUATION971 V2 EN-US
where:
Z The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific
bANSI
C class (W)
U The secondary terminal voltage for the specific C class (V)
ANSI
The CTs according to class C must have a calculated rated equivalent limiting
secondary e.m.f. E
alANSI
>
E maximum of E
alANSI
EQUATION1384 V2 EN-US
A CT according to ANSI/IEEE is also specified by the knee point voltage
U that is graphically defined from an excitation curve. The knee point
kneeANSI
voltage U normally has a lower value than the knee-point e.m.f. according
kneeANSI
to IEC and BS. U
kneeANSI
corresponding E according to IEC 61869-2. Therefore, the CTs according to
al
ANSI/IEEE must have a knee point voltage U
> ×
V 0.75 (max imum of E
kneeANSI
EQUATION2101 V2 EN-US

Voltage transformer requirements

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.
= × × +
U 20 I R
ANSI sr ct
that fulfils the following:
alreq
can approximately be estimated to 75 % of the
kneeANSI
)
alreq
1MRK 506 375-UEN A
can be
alANSI
× ×
20 I Z
sr bANSI
(Equation 94)
(Equation 95)
that fulfills the following:
(Equation 96)
Railway application RER670 2.2 IEC
Application manual
M11608-3 v5