ABB Relion 670 series - Page 926

sn
R
al a lreq CT L
2
pn n
k ma x
I I
S
E E R R
I I
³ = × + +
æ ö
×
ç ÷
è ø
EQUATION1675 V1 EN (Equation 536)
sn
R
al alreq CT L
2
pn n
kzone1
I I
S
E E R R
I I
³ = × + +
æ ö
×
ç ÷
è ø
EQUATION1676 V1 EN (Equation 537)
where:
I
kmax
Maximum primary fundamental frequency current for close-in forward and reverse
faults (A)
I
kzone1
Maximum primary fundamental frequency current for faults at the end of zone 1
reach (A)
I
pr
The rated primary CT current (A)
I
sr
The rated secondary CT current (A)
I
n
The nominal current of the protection IED (A)
R
ct
The secondary resistance of the CT (W)
R
L
The resistance of the secondary wire and additional load (W). In solidly grounded
systems the loop resistance containing the phase and neutral wires should be used
for phase-to-ground faults and the resistance of the phase wire should be used for
three-phase faults.
In isolated or high impedance grounded systems the resistance of the single
secondary wire can always be used.
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
Table continues on next page
Section 25 1MRK 506 369-UUS -
Requirements
920 Line distance protection REL670 2.2 ANSI
Application manual