ABB REG670 Applications Manual

Where:
I
f
Maximum primary fundamental frequency three-phase fault current that passes the
CTs (A)
R
L
The resistance of the secondary wire and additional load (Ω). The loop resistance
containing the phase and neutral wires shall be used.
24.1.7 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
al
according to the IEC 61869-2 standard. From
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
al
. By
comparing this with the required rated equivalent limiting secondary e.m.f. E
alreq
it is
possible to judge if the CT fulfills the requirements. The requirements according to
some other standards are specified below.
24.1.7.1 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
ALF
.
The value of the E
ALF
is approximately equal to the corresponding E
al
. Therefore, the
CTs according to class P and PR must have a secondary limiting e.m.f. E
ALF
that
fulfills the following:
ALF alreq
E max E
EQUATION1383 V4 EN
(Equation 312)
24.1.7.2 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
knee
(E
k
for class PX and PXR, E
kneeBS
for class X and the limiting
secondary voltage U
al
for TPS). The value of the E
knee
is lower than the corresponding
E
al
according to IEC 61869-2. It is not possible to give a general relation between the
E
knee
and the E
al
but normally the E
knee
is approximately 80 % of the E
al
. Therefore,
the CTs according to class PX, PXR, X and TPS must have a rated knee point e.m.f.
E
knee
that fulfills the following:
( )
knee k kneeBS al alreq
E E E U 0.8 maximum of E» » » > ×
EQUATION2100 V2 EN
(Equation 313)
1MRK 502 071-UEN - Section 24
Requirements
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 757
Application manual

ABB REG670 Specifications

General

Brand	ABB
Model	REG670
Category	Protection Device
Language	English