(Equation 398)
The delayed inverse reset time depends also on the protection function's start
duration value START_DUR. The reset time on the drop-off moment can be
calculated by multiplying t[s] with START_DUR.
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
1MRS759142 F
General function block features
REX640
Technical Manual
1895