Toshiba GR200 Series Instruction Manual page 82

DIFL operations for 1.5CB arrangement
The DIFL function may be used to protect a line that is connected with busbars in a one-and-
a-half breaker arrangement (1.5CB). Therefore, the DIFL function has protection features for
a stub fault and a through-fault-current countermeasure†. Additionally, the user should have
special attentions for the DIFL settings when an outflow current flows on the adjacent line,
provided the parallel lines are configured in the 1.5CB.
†Note: Scheme switch [DIFL-CTSat] Non is also required for the through-fault
counter measure when the DIFL operates in the 1.5CB arrangement. For more
information, see section 2.4.2(iii)
Through-fault-current encountered by DIF (TFC in DIFL and DIFGL)
2.6.1
Figure 2.6-1 shows a one-and-a-half CB arrangement (1.5CB). We assume that a close-in fault
occurs externally. A fault-current (I G ) may flow very much on the current transformers (CT1 G
and CT2 G ) at the terminal-G, whereas another fault-current (I H ) may flow a little on the other
current transformers (CT1 H and CT2 H ) at the terminal-H. Consequently, the through-fault
current may cause a differential current (Id) erroneously in the DIFL function if the CT1 G
characteristic is not identical to the CT2 G characteristic.
CT1
I
G1
CB
CB
I
G2
CT2
I I
G H
I +I I +I
= G1 G2 = H1 H2
CB
Close-in fault
Terminal-G
Figure 2.6-1 Through-fault-current flowing in an external close-in fault
G
Transmission line GH
G
Current data
IED_G
Current data
Communication channels
- 59 -
6F2S1914 (0.49)
CT1
H
I
H1
CB
CB
I
CT2
H2
H
IED_H
CB
Terminal-H
GRL200 (Soft 033 & 037)