Toshiba GR200 Series Instruction Manual page 78

Setting DIFL accounting for CT ratio/rating and fault currents
The user should take coordination about the DIFL settings when the difference exists between
the CT ratios at the local-terminal and at the remote-terminal. Additionally, the user should
consider a minimum fault current for the internal fault and an earth fault current flowing in
a high-impedance for grounding. The user should note that the monitoring values—currents
at the local and the remote-ends (Ia-L, Ia-R1, etc.) and differential currents (Id), which are
shown in Chapter
procedures below has been performed.
Nature of CT ratios matching
2.5.1
DIFL setting for CT ratios being identical
(i)
In the foregoing discussions, the DIFL settings at the local and remote-terminals are made,
which are based on the assumption that the detection thresholds of a fault current are identical
for the both terminals. Figure 2.5-1 exemplifies settings of the DIFL functions having the
assumption; the DIFL sensitivity is taken account of 800 A in terms of the primary side of the
CT. Thereby, at the both terminals, the settings ([DIFL-I1], [DIFL-I2] and others) have to be set
identically.
Busbar-G
CT ratio:
2000/1 A
DIFL
Setting [DIFL-I1] =
Figure 2.5-1 Setting example when ratios being identical
DIFL setting for CT ratios being not identical
(ii)
When the CT ratio at the remote-terminal is not identical to the CT ratio at the local-terminal,
the user should make matching ratios between two CTs. Figure 2.5-2 shows the two different
CTs are arranged on the line GH. Thereby, for example, the user should have a setting [DIFL-
I1] at terminal-G and another setting [DIFL-I1] at terminal-H. In like manner, we have different
setting values for [DIFL-I2] and others.
Monitoring function
—will not screened and recorded even if matching
DIFL sensitivity required on line GH
= 800A on the primary current
Sensitivity (primary)
CT ratio
800 A
=
2000 / 1 A
= 0.4 A
- 55 -
CT ratio:
2000/1 A
DIFL
Sensitivity (primary)
Setting [DIFL-I1] =
CT ratio
800 A
=
2000 / 1 A
= 0.4 A
6F2S1914 (0.49)
Busbar-H
GRL200 (Soft 033 & 037)