ABB RELION RET670 - Distance Protection

sn R
al alreq CT L
2
pn n
f
I
S
E E I R R
I I
³ = × + +
æ ö
×
ç ÷
è ø
EQUATION1674 V1 EN-US (Equation 518)
where:
I
f
Maximum primary fundamental frequency current that passes two main CTs without passing the
power transformer (A)
25.1.6.2 Distance protection
M11619-3 v5
The current transformers must have a rated equivalent limiting secondary e.m.f. E
al
that is lar
ger than the maximum of the required rated equivalent limiting secondary
e.m.f. E
alreq
below:
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-US (Equation 519)
sn
R
al alre q CT L
2
pn n
kzone1
I I
S
E E R R
I I
³ = × + +
æ ö
×
ç ÷
è ø
EQUATION1676 V1 EN-US (Equation 520)
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
1MRK 504 163-UUS A Section 25
Requirements
Transformer protection RET670 2.2 ANSI 989
Application manual