Toshiba GR200 Series Instruction Manual page 42
Centralized busbar protection ied
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DIF slope settings
2.1.5
As shown in Figure 2.1-1, the user is able to program a slope factor (k) arbitrary using the
settings [DIFCH-Slope] and [DIFDZ-Slope], but the values are recommended to set 30%
generally. Table 2.1-2 illustrates the reason. The user has to note the operation performance
can get worse when the setting value is less than 30% in the same circumstances.
Table 2.1-2 Choice of the slope factor [DIF*-Slope] in DIF characteristic
Choice of slope factor (k)
Lager than 30%
Smaller than 30 %
Operation for half-current leaving fault
(i)
When a leaving current (=1) is a half of entering currents (=2) (that is, half current-
leaving fault), the DIF operation is pointed at the black circle in Figure 2.1-8. In accordance
with the Id-Ir characteristic, the fault can be detected with the setting [DIF**-Slope]†=30%
because of the ratio of Id/Ir = 1/3.
Id
3
Setting[DIFCH-I]
Figure 2.1-8 DIF operation on half current-leaving fault
Factor for no-change period
(ii)
As CT saturation detection is discussed in section 2.1.3(i), the detection ratio of the no-
change-period (i.e., CT saturation detection performance) can be defined under CT
requirements and the conditions of external faults. Detection ratio (i.e., 15% fixed in Equation
(2.1-1)) is applied to determine the current transfer requirements (section 2.1.4).
Note: 20% or larger value has to be chosen for the setting [DIF**-Slope], so that the DIF
function is able to operate maintaining the CT saturation detection performance.
If a small value (i.e., less than 20%) is chosen, the DIF function may fail to operate
correctly for fault occurrences. This is because; an overlap area can be raised for
blocking CT saturation detection.
Operation effects in DIF computation
Depending busbar arrangements or CB operating conditions, the
DIF is unable to detect a 'half current-leaving fault'.
The detection to detect CT saturation is degraded; as a result, the
CT requirement can be decayed.
Operating area
Half current-leaving fault
(Id/Ir=1/3)
)
10
- 28 -
CB Closed
CB Closed
CB Closed
Ir
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)
6F2S1931 (0.20)
Id＝1
Ir＝3
CB Open
Half current-leaving fault
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