Directional Phase And Residual Overcurrent Protection - ABB REC670 Applications Manual

Section 24
Requirements
24.1.6.4
24.1.7
24.1.7.1
604

Directional phase and residual overcurrent protection

If the directional overcurrent function is used the CTs must have a rated equivalent
limiting secondary e.m.f. E
equivalent limiting secondary e.m.f. E
³ = ×
E E I
al alreq k max
EQUATION1078 V2 EN-US
where:
I Maximum primary fundamental frequency current for close-in forward and reverse faults (A)
kmax
I The rated primary CT current (A)
pr
I The rated secondary CT current (A)
sr
I The rated current of the protection IED (A)
r
R The secondary resistance of the CT (W)
ct
R The resistance of the secondary cable and additional load (W). The loop resistance
L
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.
S The burden of an IED current input channel (VA). S
R
S =0.150 VA/channel for I
R
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
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 . By comparing this with the required rated equivalent limiting secondary e.m.f.
al
E it is possible to judge if the CT fulfills the requirements. The requirements
alreq
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
the CTs according to class P and PR must have a secondary limiting e.m.f. E
that fulfills the following:
that is larger than or equal to the required rated
al
below:
alreq
æ ö
I S
× + +
sr
R
R R
ç ÷
ct L
2
I
I
è ø
pr
r
=5 A
r
according to the IEC 61869-2
al
1MRK 511 401-UEN A
(Equation 132)
=0.020 VA/channel for I =1 A and
R r
. Therefore,
al
Bay control REC670 2.2 IEC
Application manual
M11624-3 v6
SEMOD53771-1 v1
M11623-4 v3
M11623-6 v4
.
ALF
ALF