ABB eVM1 Installation And Service Instructions Manual page 71

Parameter
Start Value DT1, Ie>
Time, te>
Start Value DT2, Ie>>
Time, te>>
The threshold setting range is expressed in primary current Ampere [A], up to tens of Ien where
Ien is the CCT Earth Nominal Primary Current value entered in the General Settings. When the
CCT presence box is not ticked, Ien is calculated by summing the three phase currents and
setting range limits are referred to In - The Nominal Primary Current.
When Ie is measured directly (by ticking CCT presence box under "General settings") Start
Value begins from 0,05 Ien.
14.7.2.3.1 Measurement mode
Earth fault definite time protection functions evaluate the RMS residual current at the
fundamental frequency in two ways:
direct measurement of earth fault current at the dedicated analog input via an external residual
current transformer (the lowest Start Value setting allowed is 0.05 Ien as the protection is more
sensitive), or
neutral current calculated by the vectorial sum of the three phase currents.
Ticking the CCT presence box in the General Settings enables the direct measurement mode.
14.7.2.3.2 Operation criteria
If the measured or calculated RMS earth current exceeds the setting threshold value (Start Value),
the earth fault protection function is started.
The protection function will return to passive status and the start signal will be cleared if the earth
current falls below 95% of the set threshold value.
After the protection has entered the start status and the preset operating time (Time) has elapsed,
the function goes into TRIP status and the trip signal is generated.
The protection function will exit the TRIP status and the trip signal will be cleared when the earth
current value falls below 40% of the setting threshold value.
An overcurrent time-step characteristic can be
generated when the two overcurrent definite time
functions are active simultaneously, as shown
in the following figure.
Fig. 62 Schematic view of the earth fault definite time tripping steps
Values Default
0,30 ... 15 p.u. di Ien 0.3 Ien
40 ... 30000 40
0,30 ... 15 p.u. di Ien 1 Ien
40 ... 30000 1000
Step Unit Explanation
1 A Earth fault Current
threshold.
10 ms Earth fault Time delay.
1 A Earth fault Current
threshold.
10 ms Earth fault Time delay.
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