ABB RELION REB670, Applications Manual

Page: 537 / 554

R
ct
The secondary resistance of the CT ( W )
R
L
The resistance of the secondary cable and additional load (
W
). The loop
resistance containing the phase and neutral wires, must be used for faults in
solidly grounded systems. The resistance of a single secondary wire should be
used for faults in high impedance grounded systems.
S
R
The burden of an IED current input channel (VA). S
R
=0.020 VA/channel for I
r
=1
A and S
R
=0.150 VA/channel for I
r
=5 A
Independent of the value of I
op
the maximum required E
al
is specified according to the
following:
s n R
a l a lre q ma x CT L
2
pn n
k ma x
I S
E E I R R
I I
³ = × + +
æ ö
×
ç ÷
è ø
EQUATION1680 V1 EN-US
(Equation 96)
where
I
kmax
Maximum primary fundamental frequency current for close-in faults (A)
21.1.7 Current transformer requirements for CTs according to other
standards
SEMOD53771-1 v1
M11623-4 v3
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.
21.1.7.1 Current transformers according to IEC 61869-2, class P, PR
M11623-6 v4
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:
1MRK 505 370-UUS A
Section 21
Requirements
Busbar protection REB670 2.2 ANSI 531
Application manual