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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
⎢
⎛
−
1
⎜
⎢
⎝
⎣
where:
t = time required for the element to reset fully after complete operation (seconds),
I = energising current (amps),
Is = overcurrent setting (amps),
kr = time required to reset fully after complete operation when the energising current is zero
(see Table 2.1.1),
RTMS = reset time multiplier setting.
b = constants defining curve.
Figure 2.1.4 illustrates the dependent time reset characteristics.
⎤
⎥
kr
⎥
(2)
b
⎥
⎞
I
⎟
⎥
⎠
I
⎦
S
⎯
⎯
13
6 F 2 S 0 7 5 8
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