ABB Relion REQ650, Руководство по применению

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E
a lANSI
20 I
s n
R
C T
U
A NSI
+
× ×
20 I
s n
R
C T
× ×
20 I
s n
Z
b ANSI
× ×
+ = =
EQUATION971 V1 EN
(Equation 87)
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 max imum of E
>
EQUATION1384 V1 EN
(Equation 88)
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:
E
kneeANSI
>
0.75 · (maximum of E
alreq
)
EQUATION2101 V1 EN
(Equation 89)
16.2 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.
The protection IED has effective filters for these transients, which gives secure and
correct operation with CVTs.
Section 16
1MRK 505 291-UEN A
Requirements
322
Application manual