ABB RED650, Applications Manual

Page: 438 / 454

CT. A corresponding rated equivalent limiting secondary e.m.f. E
alANSI
can be
estimated as follows:
alANSI sr ct ANSI sr ct sr bANSI
E 20 I R U 20 I R 20 I Z
= × × + = × × + × ×
EQUATION971 V2 EN-US
(Equation 141)
where:
Z
bANSI
The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific
C class (
W
)
U
ANSI
The secondary terminal voltage for the specific C class (V)
The CTs according to class C must have a calculated rated equivalent limiting
secondary e.m.f. E
alANSI
that fulfils the following:
alANSI alreq
E maximum of E
>
EQUATION1384 V2 EN-US
(Equation 142)
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 143)
22.2 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.
Section 22
1MRK 505 393-UEN B
Requirements
432 Line differential protection RED650 2.2 IEC
Application manual