Toshiba GR200 Series Instruction Manual page 217

Characteristic of directional OCN in the reverse
(iii)
The reverse characteristic is a mirror image of the forward characteristic. The setting and the
scheme switch, in addition to providing the setting of the directional OCN element in the
forward direction, provides the setting of the directional EF element in the reverse direction:
for example, Reverse is set for the scheme switch [OCN1-Dir] when the direction of the OCN
element for stage 1 is considered.
Inverse time and definite time delay characteristic
2.7.2
The OCN element monitors the negative-sequence current; when the negative-sequence
current is beyond the threshold for the operation, the OCN element will operate within a period
that is defined by the time characteristic feature. The user can choose the one of the operate
time delay characteristics: (i) dependent (inverse) time characteristic delay (i.e., IDMT) or (ii)
independent (definite) time characteristic delay (i.e., DT). The operate time of the IDMT
depends upon the level of the negative-sequence current, whereas the operate time in the DT
is a constant.
For the reset time delay in the IDMT, either inverse (dependent)-time-reset or
definite(independent)-time-reset is characterized by the setting.
The user can select which characteristic will be applied to each stage of the OCN
element using scheme switches. We shall see the scheme switches later.
DT characteristic
(i)
The operate time in the DT characteristic will be a constant time; it is not affected by the level
of the negative-sequence current. The reset time is set to zero so that resetting is performed
immediately. The user can set the operate time using a setting; it is discussed in sections (iv).
IDMT characteristic
(ii)
The operate time in the IDMT characteristic is inversely proportional to the level of the fault
current. The user can choose the operate time from a preset curve. Ten characteristic curves
are available; i.e. nine pre-installed curves covering IEC, IEEE, US and UK standard
characteristic curves and one original (user programmable) characteristic curve for which the
user can set the equation parameters. The IDMT curve equation and parameters will be
explained in section (iii).
The reset time of the IDMT is also user-selectable; either inverse-time-reset or definite-
time-reset is selected. For the inverse-time-rest, the user can choose the reset time for the
preset characteristic from six characteristic curves; i.e. IEEE and US standard five pre-
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6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)