External Faults On C-4 - GE B90 Instruction Manual

10 APPLICATION OF SETTINGS
Table 10–6: CALCULATIONS FOR THE EXTERNAL FAULTS ON C-3
CT I (KA)
FAULT
CT-2 0
CT-3 8.0
CT-4 5.0
CT-6 3.0
CT-7, CT-8 8.0
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.
Table 10–7: EXTERNAL FAULT CALCULATIONS ON C-4
CT I (KA)
FAULT
CT-1 0
CT-2 0
CT-3 6.0
CT-4 9.0
CT-6 3.0
CT-7, CT-8 9.0
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.
Table 10–8: EXTERNAL FAULT CALCULATIONS ON C-5
CT I (KA)
FAULT
CT-1 0
CT-2 0
CT-3 6.0
CT-4 5.0
CT-5 11.0
CT-7, CT-8 11.0
GE Multilin
I (A SEC) T (MS)
FAULT DC
0.00 N/A
33.33 40
25.00 30
15.00 40
33.33 40
I (A SEC) T (MS)
FAULT DC
0.00 N/A
0.00 N/A
25.00 5
45.00 40
15.00 40
37.50 40
I (A SEC) T (MS)
FAULT DC
0.00 N/A
0.00 N/A
25.00 5
25.00 30
55.00 30
45.83 30
B90 Low Impedance Bus Differential System
10.4 SLOPES AND HIGH SET THRESHOLD
AC DC
SATURATION SATURATION
No No
No Yes
No Yes
No Yes
No Yes

10.4.5 EXTERNAL FAULTS ON C-4

AC DC
SATURATION SATURATION
No No
No No
No No
No Yes
No Yes
No Yes
10.4.6 EXTERNAL FAULTS ON C-5
AC DC
SATURATION SATURATION
No No
No No
No No
No Yes
No Yes
No Yes
T (MS)
SAT
N/A
23.68
26.37
61.50
23.68
T (MS)
SAT
N/A
N/A
N/A
10.03
61.50
22.23
T (MS)
SAT
N/A
N/A
N/A
10
26.37
9.45
11.54
10-9