3
Using the MegaPulse Impulse Tester
The impulse test involves high voltage and caution should be exercised when using the tester. The
RETURN
lead is referenced to building ground when properly connected. However, the
OUTPUT
and
RETURN
leads
must always be treated as Hazardous whenever the power switch of the MegaPulse is in the ON position.
The MegaPulse impulse tester generates the impulse waveform only; it does not determine Passing or
Failing results. It is the operator’s responsibility to monitor the output waveform and determine Passing or
Failing results. In monitoring the impulse waveform, consider the following points:
The Impulse waveform is high voltage, and high frequency (short duration). Always ensure that the
measuring instrument (usually an oscilloscope with a high-voltage probe) is rated for the voltage involved,
and that the frequency response of the instrument and probe are capable of measuring the output waveform
of the MegaPulse Impulse Tester. A measuring instrument or probe with a low frequency response will result
in erroneous readings that could be mis-read.
Pressing the POLARITY switch on the front panel can change the polarity of the output waveform. The
polarity is Normal when the
NOR
indicator is lit. In this case, the high voltage will appear on both
OUTPUTS
as a positive pulse relative to the
RETURN
jack. When the polarity switch is in the Reverse
position (
REV
indicator is lit), the high voltage will appear on both
OUTPUTS
as a negative pulse relative
to the
RETURN
jack. The polarity switch only operates when the
CHARGE
LED is lit, i.e. the output is
not charged.
Note that the voltage meter may indicate that some residual voltage is present on the main storage capacitor,
even when the tester is first turned ON. This is due to inherent charging of the internal capacitors. Pressing
the
TRIGGER
switch will discharge the capacitors (be sure not to touch the output and return leads when
pressing the trigger switch).
Note that the peak amplitude of the measured output waveform is proportional to the voltage that is read on
the front panel of the MegaPulse. Therefore, it is important to measure the peak amplitude of the output
waveform and adjust the output of the MegaPulse accordingly.
Determination of Passing and Failing results can prove difficult. To obtain the most accurate results, it is
generally necessary to perform multiple impulse tests on a few different test samples (that have adequate
insulation to pass the impulse test). Take note of the impulse waveshape, amplitude, and duration. Also note
how much variance there is in the waveshape from test to test. Also (if possible), perform impulse testing on
some test samples that are known to have inadequate (or damaged) insulation. Take note of the impulse
waveshape, amplitude, and duration, when an insulation breakdown occurs.
