Current Transformer Requirements For Cts According To Other Standards; Current Transformers According To Iec 61869-2, Class P, Pr; Current Transformers According To Iec 61869-2, Class Px, Pxr (And Old Iec 60044-6, Class Tps And Old British Standard, Class X) - ABB Relion REC670 Applications Manual

Section 22
Requirements
³
E E
al
EQUATION1078 V2 EN-US
where:
I
kmax
I
pr
I
sr
I
r
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
available data for relaying applications it is possible to approximately calculate a secondary
e.m.f. of the CT comparable with E
limiting secondary e.m.f. E
requirements according to 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
E is approximately equal to the corresponding E
alf
and PR 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
U for TPS). The value of the E
al
61869-2. It is not possible to give a general relation between the E
the E
knee
TPS must have a rated knee point e.m.f. E
462
æ
I
= × ×
sr
I R
ç
alreq k max ct
I
è
pr
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 earthed systems. The resistance of a single
secondary wire should be used for faults in high impedance earthed systems.
The burden of an IED current input channel (VA). S
channel for I =5 A
r
according to the IEC 61869-2 standard. From different standards and
al
it is possible to judge if the CT fulfills the requirements. The
alreq
>
max E
alreq
(E for class PX and PXR, E
knee k
knee
is approximately 80 % of the E
ö
S
+ +
R
R
÷
L
2
I
ø
r
=0.020 VA/channel for I
R
. By comparing this with the required rated equivalent
al
. Therefore, the CTs according to class P
al
that fulfills the following:
alf
for class X and the limiting secondary voltage
kneeBS
is lower than the corresponding E
. Therefore, the CTs according to class PX, PXR, X and
al
that fulfills the following:
knee
1MRK 511 358-UEN A
(Equation 135)
=1 A and S =0.150 VA/
r R
SEMOD53771-1 v1
. The value of the
alf
(Equation 136)
according to IEC
al
and the E but normally
knee al
Application manual
M11623-4 v3
M11623-6 v3
M11623-14 v5