ABB Relion 670 Series Applications Manual page 514

Section 22
Requirements
³
E E
a l a lre q
EQUATION1681 V1 EN-US
where:
I
kmax
I
pr
I
sr
I
n
R
ct
R
L
S
R
22.1.7 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
data for relaying applications it is possible to approximately calculate a secondary e.m.f. of the CT
comparable with E
e.m.f. E
alreq
some other standards are specified below.
22.1.7.1 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
is approximately equal to the corresponding E
must have a secondary limiting e.m.f. E
E
2 max
EQUATION1383 V3 EN-US
22.1.7.2 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
TPS). The value of the E
508
æ
I
×
= × +
s n
I R R
ç
k ma x
CT
I
è
pn
Maximum primary fundamental frequency current for close-in forward and reverse faults (A)
The rated primary CT current (A)
The rated secondary CT current (A)
The rated current of the protection IED (A)
The secondary resistance of the CT (W)
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.
The burden of an IED current input channel (VA). S
for I =5 A
r
according to the IEC 61869-2 standard. From different standards and available
al
. By comparing this with the required rated equivalent limiting secondary
al
it is possible to judge if the CT fulfills the requirements. The requirements according to
>
max E
alreq
(E for class PX and PXR, E
k
is lower than the corresponding E
knee
ö
S
+
R
÷
L
2
I
ø
n
=0.020 VA/channel for I
R
. Therefore, the CTs according to class P and PR
al
that fulfills the following:
alf
for class X and the limiting secondary voltage V
kneeBS
1MRK 511 358-UUS A
=1 A and S =0.150 VA/channel
r R
. The value of the E
alf
according to IEC 61869-2. It is not
al
Application manual
(Equation 136)
SEMOD53771-1 v1
M11623-4 v3
M11623-6 v3
alf
(Equation 137)
M11623-14 v5
for
al