ABB RED650, Applications Manual

Page: 434 / 454

sr R
al alreq t max ct L
2
pr
r
I S
E E 2 I R R
I I
æ ö
³ = × × × + +
ç ÷
è ø
EQUATION1410 V2 EN-US
(Equation 133)
where:
I
kmax
Maximum primary fundamental frequency fault current for internal close-in faults
(A)
I
tmax
Maximum primary fundamental frequency fault current for through fault current
for external 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 wire 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
In substations with breaker-and-a-half or double-busbar double-breaker
arrangement, the through fault current may pass two main CTs for the line
differential protection without passing the protected line. In such cases and if both
main CTs have equal ratios and magnetization characteristics the CTs must satisfy
equation
132 and equation 134 .
sr R
al alreq tfdb ct L
2
pr
r
I S
E E I R R
I I
æ ö
³ = × × + +
ç ÷
è ø
EQUATION1411 V2 EN-US
(Equation 134)
where:
I
tfdb
Maximum primary fundamental frequency through fault current that passes two main CTs
(one-and-a-half or double-breaker) without passing the protected line (A)
If a power transformer is included in the protected zone of the line differential
protection the CTs must also fulfill equation
135 .
Section 22
1MRK 505 393-UEN B
Requirements
428 Line differential protection RED650 2.2 IEC
Application manual