Toshiba GR200 Series Instruction Manual page 269

Characteristic of directional EF in the reverse direction
(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 EF 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 [EF1-Dir] when the direction of the EF element
for stage 1 is considered.
Inverse time and definite time delay characteristic
2.16.2
The EF element monitors the earth-fault currents; when one of the currents is beyond the
threshold for the operation, the EF element will operate within a period that is defined by the
time characteristic feature. The user can choose the EF operate time delay characteristics,
either dependent (inverse) time characteristic delay (i.e., IDMT) or independent (definite) time
characteristic delay (i.e., DT). The operate time of the IDMT depends upon the level of the
energizing current, and 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 EF
element by setting a scheme switch. We shall see the scheme switches later.
DT characteristic
(i)
The operate time in the DT characteristic will be a constant time and is not affected by the
level of 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 section (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 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-installed
characteristic curves and one user original characteristic carver where the user can set the
equation parameters. The inverse-time-reset curve equation and parameters will be discussed
- 246 -
6F2S1914 (0.49)
GRL200 (Soft 033 & 037)