11.2.1
IDMT curves for overcurrent protection
In inverse-time modes, the operation time depends on the momentary value of the
current: the higher the current, the faster the operation time. The operation time
calculation or integration starts immediately when the current exceeds the set
Start
value and the
START
output is activated.
The
OPERATE
output of the component is activated when the cumulative sum
of the integrator calculating the overcurrent situation exceeds the value set by
the inverse-time mode. The set value depends on the selected curve type and
the setting values used. The curve scaling is determined with the
Time multiplier
setting.
There are two methods to level out the inverse-time characteristic.
• The
Minimum operate time setting defines the minimum operating time for the
IDMT curve, that is, the operation time is always at least the
Minimum operate
time setting.
• Alternatively, the
IDMT Sat point is used for giving the leveling-out point as a
multiple of the
Start value setting. (Global setting: Configuration > System >
IDMT Sat point). The default parameter value is 50. This setting affects only the
overcurrent and earth-fault IDMT timers.
IDMT operation time at currents over 50 x In is not guaranteed.
1MRS757644 H
General function block features
620 series
Technical Manual
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