Directional Phase And Residual Overcurrent Protection - ABB REC670 Applications Manual

Section 24
Requirements
24.1.6.4
634
R
The secondary resistance of the CT (W)
ct
R The resistance of the secondary cable and additional load (W). The loop
L
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.
S The burden of an IED current input channel (VA). S
R
A and S
Independent of the value of I
following:
I
×
³ =
E E I s n
k ma x
a l a lre q ma x
I
pn
EQUATION1680 V1 EN-US
where
I Maximum primary fundamental frequency current for close-in faults (A)
kmax

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
limiting secondary e.m.f. E
I
×
³ = ×
E E I s n
k ma x
a l a lre q
I
pn
EQUATION1681 V1 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)
n
R The secondary resistance of the CT (W)
ct
R The resistance of the secondary cable and additional load (W). The loop resistance containing the
L
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.
S The burden of an IED current input channel (VA). S
R
VA/channel for I =5 A
r
=0.150 VA/channel for I =5 A
R r
the maximum required E
op
æ ö
S
× + +
R R R
ç ÷
CT L
2
I
è ø
n
that is larger than or equal to the required rated equivalent
al
below:
alreq
æ ö
S
+ +
R R R
ç ÷
CT L
2
I
è ø
n
1MRK 511 401-UUS A
=0.020 VA/channel for I
R
is specified according to the
al
=0.020 VA/channel for I =1 A and S
R r
Bay control REC670 2.2 ANSI
Application manual
=1
r
(Equation 131)
M11624-3 v6
(Equation 132)
=0.150
R