ABB RED650, Applications Manual

Page: 435 / 454

sr R
al alreq rt ct L
2
pr r
I S
E E 30 I R R
I
I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1412 V2 EN-US
(Equation 135)
where:
I
rt
The rated primary current of the power transformer (A)
22.1.6.2 Distance protection
M11619-3 v5
The current transformers must have a rated equivalent limiting secondary e.m.f. E
al
that is larger than the maximum of the required rated equivalent limiting secondary
e.m.f. E
alreq
below:
k max sr R
al alreq ct L
2
pr
r
I I S
E E a R R
I
I
×
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1080 V2 EN-US
(Equation 136)
kzone1 sr R
al alreq ct L
2
pr r
I I S
E E k R R
I I
×
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1081 V2 EN-US
(Equation 137)
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
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 wire and additional load (
W
). In solidly earthed
systems the loop resistance containing the phase and neutral wires should be
used for phase-to-earth faults and the resistance of the phase wire should be
used for three-phase faults.
In isolated or high impedance earthed 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 505 393-UEN B
Section 22
Requirements
Line differential protection RED650 2.2 IEC 429
Application manual