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Undercurrent Protection
I< (37)
Directional earth fault
protection I
> (67N)
dir
The undercurrent unit measures the fundamental frequency
component of the phase currents.
The stage I< can be configured for definite time characteristic.
The undercurrent stage is protecting rather the device driven by the
motor e.g. a submersible pump, than the motor itself.
Table 3.15 – Parameters of the undercurrent stage: I< (37)
Parameter
Measured
ILmin
value
Setting
I<
values
t<
Recorded
SCntr
values
TCntr
Type
Flt
Load
EDly
The directional earth fault protection is used for earth faults in
networks or motors where a selective and sensitive earth fault
protection is needed and in applications with varying network
structure and length.
The device consists of versatile protection functions for earth
fault protection in various network types.
The function is sensitive to the fundamental frequency
component of the residual current and zero sequence voltage and
the phase angle between them. The attenuation of the third
harmonic is more than 60 dB. Whenever the size of I
and the phase angle between I
the stage picks up and a start signal is issued. If the fault
situation remains on longer than the user's operation time delay
setting, a trip signal is issued.
Protection Functions
Value/unit
Description
A
Min. value of phase currents IL1...IL3 in
primary value
xImode
Setting value as per times Imot
S
Operation time [s]
Start counter (Start) reading
Trip counter (Trip) reading
1-N, 2-N
Fault type/single-phase fault e.g.: 1-N =
fault on phase L1
3-N
1-2, 2-3
Fault type/two-phase fault
1-3
e.g.: 2-3 = fault between L2 and L3
1-2-3
Fault type/three-phase fault
%
Min. value of fault current as per times
Imot
%
1s mean value of pre-fault currents IL1—
IL3
%
Elapsed time as compared to the set
operate time, 100% = tripping
and U
fulfils the pick-up criteria,
0
0
3-23
and U
0
0
857-UM001A-EN-P – July 2009
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