Toshiba GRL100-701B Instruction Manual page 28

Figure 2.2.10.1 Fault Current Outflow in Internal Fault
The larger current outflows from terminal C when the fault location is closer to terminal B and
the power source behind terminal C is weaker. In case of a double-circuit three-terminal line,
50% of the fault current flowing in from terminal A can flow out from terminal C if terminal C is
very close to the junction and has no power source behind it.
These outflows must be considered when setting the differential element.
CT saturation for an external fault condition
In case of a two-terminal line, the magnitude of infeeding and outflowing currents to the external
fault is almost the same. If the CTs have the same characteristics at the two terminals, the CT
errors are offset in the differential current calculation.
A
A
Case 1
A
Open
Case 2
A
Case 1
Open
Case 2
Figure 2.2.10.2 Fault Current Distribution
 27 
F B
J
C
B
F
J
C
B
F
J
C
B
F
J
C
6 F 2 S 0 8 5 0