26
As current flows from the Transmitter and through the fault, an earth voltage gradient field is
created. It is center is at the fault. This gradient field has a pattern such as that depicted in
Figure 5-2
. (Looks like the ripples in a pond when you throw a rock in, or the rings of the
stump of a tree.)
Figure 5-2: Signal Pattern Around Fault and Ground Point.
The Receiver compares the readings taken by the two probes and determines the direction and
size of the fault. Directional blinking arrows guide the operator to the exact source of the
fault. The A-Frame’s bar graph and numerical Active LCD display indicates the relative
distance to the fault and it is size.
5.1.1. Earth Voltage Gradient
Note in
Figure 5-2
that the gradient pattern appears to be concentric circles near the fault.
Properly interpreting this pattern is the key to successful operation of the 480BSFL unit.
5.1.2.
Equipotentials
The circles shown in
Figure 5-2
represent lines of equal voltage. The boxes show what the
bar graph will display with the A-Frame in different positions. Thus, if the A-Frame were
inserted so that both of the ground spikes were on the same circle, there would be no
difference in voltage between them. The bar graph will show zero, the arrows will become
erratic and the numerical Active display will show a zero. One of these positions occurs
when the fault is directly between the spikes.
