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 earthed systems. The resistance of a single secondary wire should be
used for faults in high impedance earthed 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:
sr
R
al
alreq max
k max
ct
L
2
pr
r
I
S
E
E
I
R
R
I
I
æ
ö
³
=
×
×
+
+
ç
÷
è
ø
EQUATION1077 V2 EN-US
(Equation 27)
where
I
kmax
Maximum primary fundamental frequency current for close-in faults (A)
16.1.6.3
Directional phase and residual overcurrent protection
M11624-3 v6
If the directional overcurrent function is used the CTs must have a rated equivalent
limiting secondary e.m.f. E
al
that is larger than or equal to the required rated
equivalent limiting secondary e.m.f. E
alreq
below:
sr
R
al
alreq
k max
ct
L
2
pr
r
I
S
E
E
I
R
R
I
I
æ
ö
³
=
×
×
+
+
ç
÷
è
ø
EQUATION1078 V2 EN-US
(Equation 28)
where:
I
kmax
Maximum primary fundamental frequency current for close-in forward and reverse faults (A)
I
pr
The rated primary CT current (A)
I
sr
The rated secondary CT current (A)
I
r
The rated current of the protection IED (A)
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 earthed systems.
The resistance of a single secondary wire should be used for faults in high impedance
earthed 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
1MRK 511 423-UEN A
Section 16
Requirements
Bay control REC650 2.2 IEC
297
Application manual
