21
SEARCHING OF THE CABLE INSULATION FAULT
The technique of search
The measuring hookup is shown on the
fi
gure.
Measuring lead from a socket B connect to a faulted wire, a lead A connect to a good wire,
a lead C connect to a cable shield. The wire with bad insulation on the far-end is connected
with good wire. On loop
АВ
the device applies test voltages refer a cable shield. Through
the B wire the direct current
fl
ow on the cable shield through faulted section resistance. Thus
there is a potential difference between plugs A and B which depends on distance to fault and
faulted section resistance. The device makes precision measurement of a potential difference
and leakage current, makes a
fi
ltration and data averaging for noise in
fl
uence elimination and
calculate the distance from a place of device connection to fault locate.
The device is allow with high accuracy to de
fi
ne distance to an insulation
fl
aw locate with defect
contact resistance from 0 to 20 MOhm. High metrological characteristics of ours BRIDGE
cause impression what it is enough to connect the device to a line and you will always receive
the accurate distance to cable fault in the result. However it is necessary to remember, what even
the ideal device is necessary to use correctly, else there can be mistakes because of incorrect
work, not because of device error. What kind of mistakes can lead to incorrect results?
Not single cable fault
The scheduled measurements on the cable have not been made in time. Thus there can be
insulation faults which the user does not guess. For example, initially one splice “has become
numb” and insulation resistance gone down to 8 MOhm. Then, some time ago another splice
has become faulted and resistance gone down to 1 MOhm. The distance from station to the
fi
rst splice is 2 km, and to the second splice is 5 km. All direct current bridges can de
fi
ne only
one fault. Two faults interfere and give the mixed result. In our case these two faults will give
a result as though one fault with resistance 890 MOhm is on distance of 2 km 625 m. It means
that the measurement mistake is 625 m.
