5.2.3.2 Functionality
The transient/intermittent earth-fault protection (INTRPTEF) is a sample based
function designed for the protection and clearance of intermittent and transient earth
faults in distribution and sub-transmission networks. Fault detection is done from the
residual current and residual voltage signals by monitoring the transients with
predefined criteria.
The operate time characteristics are according to definite time (DT).
The function contains a blocking functionality. Blocking deactivates all outputs and
resets timers.
5.2.3.3 Application
INTRPTEF is a dedicated earth-fault function to operate in intermittent and transient
earth faults occurring in distribution and sub-transmission networks. The function
has selectable modes for corresponding fault types. As the function has a dedicated
purpose for these fault types, fast detection and clearance of the faults can be achieved.
Intermittent earth fault in compensated networks
An intermittent earth fault is a special type of fault that is encountered especially in
compensated networks with underground cables. With underground distribution
cables, the wire insulators may get damaged due to short transients in I
0
and rapid
changes in U
0
caused by water creating a connection between the connector and the
ground. This can be characterized as a series of cable insulation breakdowns because
of the reduced voltage withstand.
A070759 V1 EN
Figure 76: Typical intermittent earth-fault residual current and residual voltage
signals on a faulty feeder
Intermittent earth-fault transients cause damping sinusoidal residual voltage. In case
of successive intermittent transients, the residual voltage level may continuously stay
high. The substation residual voltage has usually been used in the substation back-up
1MRS756378 D Section 5
Protection functions
REF615 155
Application Manual
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