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
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