GE b30

9-10 B30 Bus Differential System GE Multilin
9.4 SLOPES AND HIGH SET THRESHOLD 9 APPLICATION OF SETTINGS
9
9.4.5 EXTERNAL FAULTS ON C-4
The following table presents the results of analysis of an external fault on circuit C-4 (C-4 is connected to the North bus; C-
3 and C-5 are connected to the South bus).
By comparing the secondary currents (column 3 in the table below) with the limits of linear operation for the CTs (column 4
in the Limits of Linear Operations of the CTs table shown earlier), it is concluded that none of the CTs saturate due to the
AC currents during this fault.
Columns 6 and 7 of the following table summarize the DC saturation threat for the fault on C-4. CT-4, CT-6, CT-7, and CT-
8 can saturate due to the DC components and can generate a spurious differential signal for both the North and South bus
relays depending on the bus configuration. The saturation does not occur before 10.03 ms and is detected by the Satura-
tion Detector.
9.4.6 EXTERNAL FAULTS ON C-5
The following table presents the results of analysis of an external fault on circuit C-5 (C-5 is connected to the North bus; C-
3 and C-4 are connected to the South bus).
By comparing the secondary currents (column 3 in the table below) with the limits of linear operation for the CTs (column 4
in the Limits of Linear Operations of the CTs table shown earlier), it is concluded that none of the CTs saturate due to the
AC currents during this fault.
Columns 6 and 7 of the following table summarize the DC saturation threat for the fault on C-5. CT-4, CT-5, CT-7, and CT-
8 can saturate due to the DC components and can generate a spurious differential signal for both the North and South bus
relays depending on the bus configuration. The saturation does not occur before 9.45 ms and is detected by the Saturation
Detector.
CT-2 0 0.00 N/A No No N/A
CT-3 8.0 33.33 40 No Yes 23.68
CT-4 5.0 25.00 30 No Yes 26.37
CT-6 3.0 15.00 40 No Yes 61.50
CT-7, CT-8 8.0 33.33 40 No Yes 23.68
Table 9–7: EXTERNAL FAULT CALCULATIONS ON C-4
CT I
FAULT
(KA) I
FAULT
(A SEC) T
DC
(MS) AC
SATURATION
DC
SATURATION
T
SAT
(MS)
CT-1 0 0.00 N/A No No N/A
CT-2 0 0.00 N/A No No N/A
CT-3 6.0 25.00 5 No No N/A
CT-4 9.0 45.00 40 No Yes 10.03
CT-6 3.0 15.00 40 No Yes 61.50
CT-7, CT-8 9.0 37.50 40 No Yes 22.23
Table 9–8: EXTERNAL FAULT CALCULATIONS ON C-5
CT I
FAULT
(KA) I
FAULT
(A SEC) T
DC
(MS) AC
SATURATION
DC
SATURATION
T
SAT
(MS)
CT-1 0 0.00 N/A No No N/A
CT-2 0 0.00 N/A No No N/A
CT-3 6.0 25.00 5 No No N/A
CT-4 5.0 25.00 30 No Yes 26.37
CT-5 11.0 55.00 30 No Yes 9.45
CT-7, CT-8 11.0 45.83 30 No Yes 11.54
Table 9–6: CALCULATIONS FOR THE EXTERNAL FAULTS ON C-3
CT I
FAULT
(KA) I
FAULT
(A SEC) T
DC
(MS) AC
SATURATION
DC
SATURATION
T
SAT
(MS)