Toshiba GR200 Series Instruction Manual page 177

Characteristic of directional OC in the reverse direction
(iii)
The reverse characteristic is a mirror image of the forward characteristic. The setting and the
scheme switch, as well as the setting of the directional OC element in the forward direction,
provides the setting of the directional OC element in the reverse direction: for example,
Reverse is set for the scheme switch [OC1-Dir] when the direction of the OC on stage 1 is
considered.
Inverse time and definite time delay characteristic
2.5.2
The OC element monitors the currents; when one of the currents is beyond the threshold of
operation, the OC element will operate within a period that is defined by the time
characteristic feature. The user can choose the OC 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 setting..
The user can select which characteristic will be applied to each stage of the OC element
by setting a scheme switch. We shall see the scheme switch later.
Operation principle
(i)
Dependent time characteristic (inverse time delay)
The inverse time OC element has an inverse time feature for both operation and resetting; for
resetting, both definite time and dependent time resetting are available.
With inverse time operation, provided that the fault current has the magnitude required
to enable the determination of the location of the fault and provided that the fluctuation in the
impedance of the power source does not affect the correct determination, an inverse time OC
function provides an effective protection. With regard to the inverse time characteristic, for
example, the function can provide a fast trip for close-in faults, but will enable a delayed trip
for remote faults. The characteristic curve of the inverse time element can be selected from
among 10 characteristic curves† in conformance with IEC, IEEE, US, and UK standards.
†Note: A user-defined 'Original' curve can also be applied in addition to the 10
predefined characteristics provided.
With dependent time resetting selected, if during the resetting period the energizing
current exceeds the threshold current of the OC element, then the OC element will pick-up.
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6F2S1915 (0.46)
GRZ200 (Soft 031 & 032)