Current Transformers According To Iec 61869-2, Class Px, Pxr (And Old Iec 60044-6, Class Tps And Old British Standard, Class X); Current Transformers According To Ansi/Ieee - ABB RELION 650 Series Applications Manual

1MRK 504 158-UEN A
18.1.7.2 Current transformers according to IEC 61869-2, class PX, PXR (and old
IEC 60044-6, class TPS and old British Standard, class X)
CTs according to these classes are specified approximately in the same way by a rated knee
point e.m.f. E
U for TPS). The value of the E
al
61869-2. It is not possible to give a general relation between the E
the E
knee
TPS must have a rated knee point e.m.f. E
»
E
knee
EQUATION2100 V2 EN-US
18.1.7.3

Current transformers according to ANSI/IEEE

Current transformers according to ANSI/IEEE are partly specified in different ways. A rated
secondary terminal voltage U
terminal voltage the CT will deliver to a standard burden at 20 times rated secondary current
without exceeding 10 % ratio correction. There are a number of standardized U
example, U
e.m.f. E
E
alANSI
EQUATION971 V2 EN-US
where:
Z
bANSI
U
ANSI
The CTs according to class C must have a calculated rated equivalent limiting secondary e.m.f.
E that fulfils the following:
alANSI
E
alANSI
EQUATION1384 V2 EN-US
A CT according to ANSI/IEEE is also specified by the knee point voltage U
graphically defined from an excitation curve. The knee point voltage U
lower value than the knee-point e.m.f. according to IEC and BS. U
estimated to 75 % of the corresponding E
according to ANSI/IEEE must have a knee point voltage U
V
kneeANSI
EQUATION2101 V2 EN-US
Application manual
(E for class PX and PXR, E
knee k
knee
is approximately 80 % of the E
(
» » > ×
E E U 0.8 maximum of E
k kneeBS al
ANSI
is 400 V for a C400 CT. A corresponding rated equivalent limiting secondary
ANSI
can be estimated as follows:
alANSI
= × × +
20 I R U
sr ct ANSI
The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class
(W)
The secondary terminal voltage for the specific C class (V)
>
maximum of E
alreq
> ×
0.75 (max imum of E
for class X and the limiting secondary voltage
kneeBS
is lower than the corresponding E
. Therefore, the CTs according to class PX, PXR, X and
al
that fulfills the following:
knee
)
alreq
is specified for a CT of class C. U
= × × + ×
20 I R 20 I
sr ct sr
according to IEC 61869-2. Therefore, the CTs
al
)
alreq
according to IEC
al
and the E
knee al
is the secondary
ANSI
ANSI
×
Z
bANSI
kneeANSI
normally has a
kneeANSI
can approximately be
kneeANSI
that fulfills the following:
kneeANSI
Section 18
Requirements
M11623-14 v5
but normally
(Equation 104)
M11623-22 v6
values for
(Equation 105)
(Equation 106)
that is
(Equation 107)
271