Voltage
IDMT Voltage
Time
UL1
UL2
UL3
IEC12000186-1-en.vsd
IEC12000186 V1 EN
Figure 226: Voltage used for the inverse time characteristic integration
Trip signal issuing requires that the undervoltage condition continues for at least the
user set time delay. This time delay is set by the parameter t1 and t2 for definite time
mode (DT) and by some special voltage level dependent time curves for the inverse
time mode (IDMT). If the start condition, with respect to the measured voltage ceases
during the delay time, and is not fulfilled again within a user defined reset time
(tReset1 and tReset2 for the definite time and tIReset1 and tIReset2pickup for the
inverse time) the corresponding start output is reset. Here it should be noted that after
leaving the hysteresis area, the start condition must be fulfilled again and it is not
sufficient for the signal to only return back to the hysteresis area. Note that for the
undervoltage function the IDMT reset time is constant and does not depend on the
voltage fluctuations during the drop-off period. However, there are three ways to reset
the timer, either the timer is reset instantaneously, or the timer value is frozen during
the reset time, or the timer value is linearly decreased during the reset time. See
figure
227 and figure 228.
Section 9 1MRK502052-UEN B
Voltage protection
484
Technical manual
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