GE Digital Energy B90, Instruction Manual, Page: 324 / 502

9-8 B90 Low Impedance 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 will 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 may saturate due to the DC components and may generate a spurious differential signal for both the North and South bus
relays depending on the bus configuration. The saturation will not occur before 5.85 ms and will be 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 will 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 may saturate due to the DC components and may generate a spurious differential signal for both the North and South bus
relays depending on the bus configuration. The saturation will not occur before 4.83 ms and will be detected by the Satura-
tion Detector.
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 5.85
CT-6 3.0 15.00 40 No Yes 35.25
CT-7, CT-8 9.0 37.50 40 No Yes 9.40
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 15.19
CT-5 11.0 55.00 30 No Yes 4.83
CT-7, CT-8 11.0 45.83 30 No Yes 7.16