External Faults On C-4 - GE B30 Instruction Manual

SLOPES AND HIGH SET THRESHOLD
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 table below summarize the DC saturation threat for the fault on C-3. CT-3, 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 23.68 ms and is detected by the
Saturation Detector.
Table 8-6: Calculations for the external faults on C-3
CT I
FAULT
CT-1 0
CT-2 0
CT-3 8.0
CT-4 5.0
CT-6 3.0
CT-7, CT-8 8.0

8.4.5 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
Saturation Detector.
Table 8-7: External fault calculations on C-4
CT I
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
8
8.4.6 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.
8-10
(kA) I (A sec)
FAULT
0.00
0.00
33.33
25.00
15.00
33.33
(kA) I (A sec)
FAULT
0.00
0.00
25.00
45.00
15.00
37.50
T (ms) AC saturation
DC
N/A No
N/A No
40 No
30 No
40 No
40 No
T (ms) AC saturation
DC
N/A No
N/A No
5 No
40 No
40 No
40 No
B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: APPLICATION OF SETTINGS
DC saturation t (ms)
SAT
No N/A
No N/A
Yes 23.68
Yes 26.37
Yes 61.50
Yes 23.68
DC saturation t (ms)
SAT
No N/A
No N/A
No N/A
Yes 10.03
Yes 61.50
Yes 22.23