Toshiba GR200 Series Instruction Manual page 155

reversal may be found when an external looped circuit exists if not for parallel lines.
(a) Direction of fault current
Forward looking element
A2
Reverse looking element
Forward looking element
B2
Reverse looking element
(b) Sequence diagram
Figure 2.3-11 (b) shows sequentially the operation of the forward looking element, the
reverse looking element, and CRL on line L2 before and after the occurrence of the current
reversal.
At terminal A2, the forward looking element does not run, but the reverse looking
element runs when the current reversal is yielded. At terminal B2, the forward looking element
runs, but the reverse looking element does not run.
Provided that the forward looking element runs at terminal A2 before the forward looking
element does not run at terminal B2. This may cause false operation of POP, UOP and BOP on
line L2.
A1 F
A
A2
:Fault current flow before CB A1 being opened
:Fault current flow after CB A1 being opened
t1
CRL
CRL
Figure 2.3-11 Current reversal phenomeon
- 134 -
B1
L1
B2
L2
t2
TREBK setting
6F2S1915 (0.46)
B
t3
TREBK setting
GRZ200 (Soft 031 & 032)