ABB eVM1, Инструкция по установке и обслуживанию

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14.7.2.3 Earth fault Definite Time Overcurrent Protection
Two earth fault overcurrent definite time protection functions are available. Each of them can be
activated independently:
Overcurrent definite time low set Earth fault DT1 (Ie>)
Overcurrent definite time high set Earth fault DT2 (Ie>>)
Start Value (Ie>>): Current threshold for earth fault condition detection.
Time (te>>): Time delay for earth fault Trip condition detection.
The operating time depends on the measured current and the selected current-time characteristic.
The formulas for the trip time according to British Standard (BS 142) and IEC 60255-3 are reported
in the chapter: IDMT Protection Time-Current Characteristics.
The protection function will exit the TRIP status, the trip signal and the counter will be cleared
when the measured current value for all the phases falls below 40% of the setting threshold value.
The overcurrent time-step characteristic shown in the next figure is obtained when the two definite
time functions are combined with the IDMT. The IDMT function is generally used to provide low
current protections with an exponential characteristic threshold.
Fig. 60 Schematic view of the definite time and IDMT tripping characteristic
Fig. 61