Definite Time Reset; Dependent Time Reset - Toshiba GRE110 Instruction Manual

grading between relays at various points in the scheme.
The inverse reset characteristic is particularly useful for providing correct coordination with an
upstream induction disc type overcurrent relay.
The definite time delayed reset characteristic may be used to provide faster clearance of intermittent
('pecking' or 'flashing') fault conditions.

Definite time reset

The definite time resetting characteristic is applied to the IEC/IEEE/US operating characteristics.
If definite time resetting is selected, and the delay period is set to instantaneous, then no intentional
delay is added. As soon as the energising current falls below the reset threshold, the element returns
to its reset condition.
If the delay period is set to some value in seconds, then an intentional delay is added to the reset
period. If the energising current exceeds the setting for a transient period without causing tripping,
then resetting is delayed for a user-definable period. When the energising current falls below the
reset threshold, the integral state (the point towards operation that it has travelled) of the timing
function (IDMT) is held for that period.
This does not apply following a trip operation, in which case resetting is always instantaneous.

Dependent time reset

The dependent time resetting characteristic is applied only to the IEEE/US operate characteristics,
and is defined by the following equation:
= ×
t RTMS
where:
t = time required for the element to reset fully after complete operation (seconds),
I = energising current (amps),
Is = overcurrent setting (amps),
k = time required to reset fully after complete operation when the energising current is zero
r
(see Table 2.1.1),
RTMS = reset time multiplier setting.
k, β, c = constants defining curve.
Figure 2.1.3 illustrates the dependent time reset characteristics.
The dependent time reset characteristic also can provide user configurable IDMT curve. If
required, set the scheme switch [M∗∗∗] to "C" and set the curve defining constants kr and β. Table
2.1.1 shows the setting ranges of the curve defining constants.
 
 
kr
 
β
 
 
−
I
 
 
1
 
I
 
S
 10 
(2)
6 F 2 T 0 1 7 2