Pxr (And Old Iec 60044-6, Class Tps And Old British Standard, Class X) - ABB REB670 Applications Manual

1MRK 505 337-UUS -
19.1.6.2
19.1.6.3
Application manual
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 (E
knee
secondary voltage V for TPS). The value of the E
al
according to IEC 61869-2. It is not possible to give a general relation between the E
and the E but normally the E
al
according to class PX, PXR, X and TPS must have a rated knee point e.m.f. E
fulfills the following:
= × + - ×
S TD S (1 TD S )
Old Calculated
EQUATION1893.ANSI V1 EN
Current transformers according to ANSI/IEEE
Current transformers according to ANSI/IEEE are partly specified in different ways. A
rated secondary terminal voltage V
secondary 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 V values for example, V
ANSI
rated equivalent limiting secondary e.m.f. E
× × +
=
20 I R V
E
S N CT
a lANS I
EQUATION1682 V1 EN
where:
Z The impedance (that is, with a complex quantity) of the standard ANSI burden for the specific C class
bANSI
(W)
V 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 that fulfils the following:
alANSI
>
E maximum of E
alANSI
EQUATION1384 V2 EN
A CT according to ANSI/IEEE is also specified by the knee point voltage V
is graphically defined from an excitation curve. The knee point voltage V
for class PX and PXR, E
k
is approximately 80 % of the E
knee
is specified for a CT of class C. V
ANSI
is 400 V for a C400 CT. A corresponding
ANSI
alANSI
= × × +
20 I R 20 I
ANS I S N CT
alreq
Section 19
Requirements
for class X and the limiting
kneeBS
is lower than the corresponding E
knee
. Therefore, the CTs
al
can be estimated as follows:
× ×
Z
S N bANS I
kneeANSI
al
knee
that
knee
(Equation 96)
is the
ANSI
(Equation 97)
(Equation 98)
that
kneeANSI
487