Megger ATEC 210415 Series, Manual

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M
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AVTM21-415Ja Rev. A June 2005
regulation curve given in Figure 9 is useful for estimating in
advance the voltage control position for each step. Then
during the test, the control can be advanced to the next
predetermined setting. This procedure gives the sharpest step
change in voltage and provides better test results than if the
control is inched to the next step.
FAULT LOCATING (BREAKDOWN TESTING)
In practice, if the apparatus being tested fails, the user may be
faced with the problem of locating the failure so that repairs
can be made. Often the failure occurs in the form of an arc-
over; that is, the apparatus will support some voltage, but
above this level a spark forms at the failure, the voltage
collapses, and the current soars.
This will usually trip out the Test Set; but if the voltage control
is set just beyond the voltage that causes arc-over, it is possible
that the arc-over will repeat several times before trip out.
During this time, the operator can look for the light and noise
generated by the spark and so locate the fault. Arc-over can be
induced quite deliberately without damage to the test set; it is
even possible to place some resistance in series with the high
voltage connection and allow the arc-over to periodically
repeat and continue for long periods of time. In some cases,
however, this result can be obtained simply by careful
adjustment of the voltage control.
As an alternate the stabilizer can be switched "IN" because it
increases the time to charge a cable without the need of an
external resistor. Trip-out will be avoided and the voltage
control setting is not as critical.
This test set is not recommended for locating faults in long
cables but it may be used occasionally for cable fault locating
on short cables (on the order of 1000 ft. or less) that arc over
at voltages of less than 15 kV.