ABB eVM1 Installation And Service Instructions Manual page 72

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14.7.2.4 Earth fault IDMT
The dependent time earth fault current protection, like the IDMT, is a time-delay function with a set
of hyperbolic current-time characteristics. One earth fault IDMT function with one out of four
selectable current-time characteristics can be activated:
Normal inverse,
Very inverse,
Extremely inverse and
Long-term inverse.
Fig. 63
Type:
Base current (Ieb):
Time multiplier (k):
The trip time is calculated according to British Standard (BS 142) when the time multiplier k is
used. When the time multiplier k is set to one (k=1) the IDMT curve is in accordance to IEC
60255-3.
Parameter Values
Type NI, VI, EI, LTI
Base Current (Ieb) 0.30 ... 2.40 p.u. di Ien
Time Multiplier (K) 0.05 ... 1.50
The threshold setting range is expressed in primary current Ampere [A], up to 2.40 Ien where Ien
is the CCT Earth Nominal Primary Current value entered in the General Settings.
When the CCT presence box is blank Ien is calculated by summing the three phase currents and
setting range limits are referred to In, the Nominal Primary Current. The lowest Start Value setting
allowed is 0.3 Ien as the protection is less sensitive).
Tripping characteristic according to the IEC 60255-3 curve definition.
Current threshold for start condition detection.
Time multiplier to vary time delay for Trip condition.
Default Step Unit
NI – –
2 Ien 1 A
1 0.05 –
ExplanationType
Tripping curve
Current threshold
Time multiplier
(BS 142).