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14.7.2.5 IDMT Protection Time-Current Characteristics
The Basic protection set provides two Overcurrent IDMT and Earth fault IDMT protection functions.
For each protection of the four current-time characteristics, Normal, Very, Extremely and Long
time Inverse can be activated one at a time:
Fig. 65
14.7.2.5.1 Overcurrent IDMT
IDMT protection function evaluates the RMS value of phase currents at the fundamental frequency.
It will be activated when phase current start conditions are true (at least one phase current value
is above 1.2 times the setting threshold value, Base current Ieb).
14.7.2.5.2 Earth fault IDMT
Earth fault IDMT function evaluates the measured or calculated RMS amount of residual current
at the fundamental frequency.
It will be activated when measured or calculated earth current start conditions are true (earth
current value is above 1.2 times the setting threshold value, Base current Ieb).
When setting the base current parameter Ieb, take care not to exceed the CB, panel or load
rated current, especially for high Nominal Primary Current values In, to avoid damage due
to overheating.
Example: In = 1000A, Ieb setting range = 200...2400A, CB rated current is 1250A.
YES:
Ieb = In = 1000A, protection starts from 1.2Ieb = 1200A < 1250A CB rated current
NO:
Ieb = 2000A, protection starts from 1.2Ieb = 2400A >> 1250A CB rated current
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