Toshiba GR200 Series Instruction Manual page 249

time is set using the OC element settings.
DT characteristic
(ii)
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 in sections (vi) and (vii).
IDMT characteristic
(iii)
The operate time in the IDMT characteristic is inversely proportional to the level of the fault
current. The user can determine 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 (iv).
The reset time in the IDMT is user-selectable; either inverse-time-reset or definite-time-
reset is selected. For the inverse-time-reset, 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 curve where the user can set the
equation parameters. The inverse-time-reset curve equation and parameters will be discussed
in section (vi).
Operate time of IDMT
(iv)
The operate time in the IDMT is defined by Equation (2.15-1). (ref. IEC 60255-151):
where:
t = operate time with constant current I (seconds),
I = operate (energizing) current (amperes),
Is = overcurrent setting (amperes),
TMS = time multiplier setting number,
k, α, c = constants defining curve.
The nine pre-programmed standard characteristic curves are defined in Table 2.15-3. In
addition, one original (user-programmable) curve can be applied. One curve can be chosen for
each OC stage. Figure 2.15-5 illustrates these characteristic curves. For example, the user
should set one for the scheme switch [OC1-Timer]. ("IEC-NI" is for IEC Normal Inverse
k
t ( I ) = TMS × {[
α
( �� ��
⁄ )
��
- 226 -
] + ��}
− 1
6F2S1914 (0.49)
(2.15-1)
GRL200 (Soft 033 & 037)