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User Manual LineTroll R400D
2.1 Adaptive detector
The measured magnetic field (B-field) is applied to an adaptive dB/dt detector.
Slow variations in the load current will not affect the detector.
A fault current will cause a rapid increase in the B-field which the detector will respond to.
The detector will now require that two conditions are satisfied:
1. The relative increase dB
exceeds a configurable level.
2. The absolute increase dB
T
is greater than a pre-set value. (Trip level)
Figure 3, magnetic field
It is important to notice that the indicator measure a B-field which is a product of the current
flowing in the feeder. The trip-setting values for short-circuit and earth faults will therefore be
indicative where the values are based on a horizontal line configuration with 1,5m line-spacing
and where the indicator is mounted 3m below the middle conductor.
In triangular, vertical or other line configurations, the distances between each phase and the
indicator will differ. This means the measured B-field change upon a fault will be different and
must be taken into consideration when trip-level is set.
B-field
B-field
NO FAULT
EARTH FAULT
I
0
= 0
I
0
≠
0
