Standards - ABB REG670 Applications Manual

1MRK 502 071-UEN -
24.1.7
24.1.7.1
24.1.7.2
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Where:
I Maximum primary fundamental frequency three-phase fault current that passes the
f
CTs (A)
R The resistance of the secondary wire and additional load (Ω). The loop resistance
L
containing the phase and neutral wires shall be used.
Current transformer requirements for CTs according to other

standards

All kinds of conventional magnetic core CTs are possible to use with the IEDs if they
fulfill the requirements corresponding to the above specified expressed as the rated
equivalent limiting secondary e.m.f. E
different standards and available data for relaying applications it is possible to
approximately calculate a secondary e.m.f. of the CT comparable with E
comparing this with the required rated equivalent limiting secondary e.m.f. E
possible to judge if the CT fulfills the requirements. The requirements according to
some other standards are specified below.
Current transformers according to IEC 61869-2, class P, PR
A CT according to IEC 61869-2 is specified by the secondary limiting e.m.f. E
The value of the E is approximately equal to the corresponding E
ALF
CTs according to class P and PR must have a secondary limiting e.m.f. E
fulfills the following:

E max E
ALF
EQUATION1383 V4 EN
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 U for TPS). The value of the E
al
E according to IEC 61869-2. It is not possible to give a general relation between the
al
E and the E but normally the E
knee al
the CTs according to class PX, PXR, X and TPS must have a rated knee point e.m.f.
E that fulfills the following:
knee
» » »
E E E U
knee k kneeBS al
EQUATION2100 V2 EN
according to the IEC 61869-2 standard. From
al
alreq
for class PX and PXR, E
k
is approximately 80 % of the E
knee
(
> ×
0.8 maximum of E
alreq
Section 24
Requirements
. Therefore, the
al
for class X and the limiting
kneeBS
is lower than the corresponding
knee
al
)
. By
al
it is
alreq
.
ALF
that
ALF
(Equation 312)
. Therefore,
(Equation 313)
757