The fault current fed to the protection shall be calculated for the fault points 3, 4, 5
and 6 (faults about 80 % out on the adjacent lines connected to the local and remote
busbar).
The fault at point 3 is calculated with minimum source impedance at substation A
and with one line out from substation B taken out of service. This results in the
current I
fault3,max.
= 1.56 kA.
The fault at point 4 is calculated with minimum source impedance at substation A
and with one line out from substation B taken out of service. This gives the current
I
fault4,max.
= 1.4 kA.
The fault at point 5 is calculated with minimum source impedance at substation B
and with one line out from substation A taken out of service. This gives the current
I
fault5,max.
= 1.56 kA
The fault at point 6 is calculated with minimum source impedance at substation B
and with one line out from substation A taken out of service. This gives the current
I
fault6,max.
= 1.35 kA.
The current setting of step 2 is, if possible, chosen as:
1.2 · max(I
fault3,4,5,6max
) ≤ I
step2
≤ 0.7 · min(I
AB,min
, I
BA,min
)
1.2 · 1.56 ≤ I
step2
≤ 0.7 · 2.50 or 1.9 ≤ I
step2
≤ 1.75
In this case, it is not possible to fulfil the requirement above. Priority is given to
selectivity, choosing setting 1900 A and accepting a small risk that short circuits
close to the remote busbar are not tripped. This is acceptable as the distance
protection normally gives sufficient coverage of the whole line and remote busbar
from zone 2.
Setting: Pickup2= 190 % of IBase which corresponds to 1 900 A.
2. Set t2 to 0.4 s
If possible the delay of step 2 should be set equal to the distance protection zone 2
(normally 0.4 s). To assure selectivity with this time delay the function should not
overreach adjacent lines out from the remote busbar and out from the local busbar.
3.1.9.4 Calculating settings for step 3
1. Set Pickup3 to 110 % of IBase
To assure that step 3 detects all short circuits on the adjacent lines out from the
remote busbar a phase-phase short circuit is applied at fault points 7 and 8. The
1MRK 506 334-UUS A Section 3
REL650 setting examples
69
Application manual
To Next Page
Loading...
