t s
D
I
I
k[ ] =
>
−
⋅
2
1
(Equation 200)
t[s] Reset time (in seconds)
k set
Time multiplier
D set
Curve parameter D
I Measured current
I> set
Start value
11.2.3 Inverse-timer freezing
When the BLOCK input is active, the internal value of the time counter is frozen at
the value of the moment just before the freezing. Freezing of the counter value
is chosen when the user does not wish the counter value to count upwards or
to be reset. This may be the case, for example, when the inverse-time function
of a protection relay needs to be blocked to enable the definite-time operation
of another protection relay for selectivity reasons, especially if different relaying
techniques (old and modern relays) are applied.
The selected blocking mode is "Freeze timer".
The activation of the BLOCK input also lengthens the minimum delay
value of the timer.
Activating the BLOCK input alone does not affect the operation of the START output.
It still becomes active when the current exceeds the set
Start value
, and inactive
when the current falls below the set
Start value
and the set
Reset delay time
has
expired.
11.3 Voltage based inverse definite minimum time
characteristics
11.3.1 IDMT curves for overvoltage protection
In inverse-time modes, the operate time depends on the momentary value of the
voltage, the higher the voltage, the faster the operate time. The operate time
calculation or integration starts immediately when the voltage exceeds the set
value of the
Start value
setting and the START output is activated.
1MRS757644 H
General function block features
620 series
Technical Manual
1153
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