Toshiba GR200 Series - 2.7.4 Nature of outflowing current in case of internal fault; (i) Account of DIFL settings for a single line with outer loop; (ii) Account of DIFL settings for parallel lines

6F2S1914 (0.49)
GRL200 (Soft 033 & 037)
- 82 -
2.7.4 Nature of outflowing current in case of internal fault
The user should consider outflows when the DIFL function is applied for the following lines:
(i) Account of DIFL settings for a single line with outer loop
Figure 2.7-10 shows a three-terminal line (lines GJ, JH, and JK) with an outer loop (loop-
circuit HK). Suppose a fault occurs on the line JH. The fault current (I
F
) flowing at the
terminal-G is divided into I
F1
and I
F2
at the junction-J, then the I
F2
re-enters into the line
JH. This is because the terminal-H is connected by the loop-circuit HK.
Terminal-G
Fault
Junction-J
Terminal-H
Terminal-K
I
F
I
F1
I
F2
I
F2
I
F2
Figure 2.7-10 Single line with three-terminals with outer loop circuit
(ii) Account of DIFL settings for parallel lines
Figure 2.7-11 shows a double-circuit line with three terminals; the outer loop is generated
when the CB on the line-GJ is open. The fault current I
F
flowing out at the terminal G divided
into I
F1
and I
F2
at the junction-J’; then the I
F2
re-enter into the line J’H’ through the parallel
line JH. The larger current outflows from the terminal-K when a fault is in close proximate
the terminal-G and the power source behind the terminal-K is weaker. In general, a half of the
fault current leaving from the terminal-G may re-enter in the line-J’H’, provided the terminal-
K is very close to the junction-J and the terminal-K does not have a power source itself.
Terminal-G
Terminal-K
CB (Open)
Terminal-H
Fault
I
F
I
F1
I
F2
I
F2
I
F2
I
F2
Junction-J
Line GJ
J
Line JH
Line G’J’
Line J’H’
Line J’K’
Line JK
Figure 2.7-11 Double lines with three-terminals