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A cable length is entered incorrectly
At de
fi
nition of an insulation fault locate the device
fi
rst of all measure a loop. Then it remembers
the cable length L in Ohms. Next step is to measure distance to an insulation fault locate. The
measuring hookups of IRK-PRO measures distance to fault locate X in Ohms. When the device
is receive the distance to fault locate X in Ohms, it will divides it into cable length L in Ohms.
Thus the device is de
fi
ning the relative distance to fault locate in thousand shares of length.
This is very accurate measurement; the tolerated error is not more than 0,001. The device
displays the result, when the cable length is not entered. This is the «Cable 100%» mode, and
the distance to fault locate is shown on the screen with accuracy of the tenth shares of percent
from cable length.
To receive the distance in meters, the device should multiply the relative distance in percents
and the entered cable length. Here we can get a mistake. In one case you enter approximate
cable length - for example, 3 400 m, and actually the cable length is 3450 m. If the fault is
locate on the middle then this 50 meters multiplied into relative distance, will give an error - 25
m. If you enter the approximate cable length, it is better to make the measurements from that
end, to which the fault is closer to minimize a mistake caused by the inexact length.
In other case you can use the device special function which counts a cable length from the
measured loop if the Cable Type and the ground temperature (item «Cable Type») are known.
However used wire speci
fi
c resistance from reference book can differ from real because of cable
manufacturing techniques. The tolerance can reach 10 % so the calculations error can reach
corresponding values. Besides there is an additional error of ground temperature de
fi
nition, and
the ground temperature varies along the cable. Try to change the entered temperature on 3-5°
С
and you will see how the result will change. You should remember that when you use function
of length calculation on Cable Type and temperature, you obviously receive approximate result.
The accurate result can be received, if you enter the accurate cable length.
It is not possible to pick up the good wire
If all wires are faulted then the good wire will be faulted too. Then this fault will interfered with
fi
rst fault and will give the result displacement aside connection of a good wire. If you measure
distance to fault from the different cable ends then the indications sum will be more than the
cable length. In a case when all wires are equally faulted, the device will always show fault on
the cables far-end, independent from what end you was made the measurement.
In that case is better to use an auxiliary cable. If there is a technical opportunity, you can end
ring the measurements through good cables - that means is to connect to a faulty wire on the
far-end the two wires from another cable and to connect them to the device (probably, through
other connections if the cable is not parallel on the faulty cable). Basically the length and mark
of an auxiliary cable are indifferent. Certainly, you must to remember that the complex spatial
con
fi
guration can cause a measurement additional error.
You can use special function of a defects relation measuring the factor K, not using the
ancillary cable. In this case it is necessary to ensure, that the wires are faulted in one pace (in
one splice), else the measurement result will be incorrect. Then you make a K measuring it is
necessary to ensure that the indications are stable. Sometimes during measurements the defect
is “dried” by a measuring voltage, and the resistances relation starts to vary. It is necessary
to measure K several times and if the indications are stable to close a loop on the far-end and
to measure distance to fault locate. Sometimes the distance measurement is made after K
measurement, but the situation has already changed, that is why the result is incorrect.
