ABB RED650 Applications Manual page 434

Section 22
Requirements
428
³ = × ×
E E 2 I
al alreq t max
EQUATION1410 V2 EN-US
where:
I Maximum primary fundamental frequency fault current for internal close-in faults
kmax
(A)
I Maximum primary fundamental frequency fault current for through fault current
tmax
for external faults (A)
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)
r
R
The secondary resistance of the CT (W)
ct
R The resistance of the secondary wire and additional load (W). The loop
L
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 The burden of an IED current input channel (VA). S
R
A and S
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.
I
³ = ×
sr
E E I
al alreq tfdb
I
pr
EQUATION1411 V2 EN-US
where:
I Maximum primary fundamental frequency through fault current that passes two main CTs
tfdb
(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.
æ ö
I S
× + +
sr R
R R
ç ÷
ct L
2
I
I
è ø
pr
r
=0.150 VA/channel for I
R r
æ ö
S
× + +
R
R R
ç ÷
ct L
2
I
è ø
r
1MRK 505 393-UEN B
=0.020 VA/channel for I
R
=5 A
Line differential protection RED650 2.2 IEC
Application manual
(Equation 133)
=1
r
(Equation 134)