SURG: High voltage surge testing
Ensures that the insulation material around the copper
wire (usually lacquer) has not been damaged during manufacture introducing
the risk of an inter-winding short circuit.
Unit of measurement, mV Seconds. Range 1mVs to 1kVs with
an impulse signal level from 100V to 5kV.
Transformers with a high number of turns using fine wire
are vulnerable to insulation damage. Damage to the insulation material
during production is very difficult to detect as there may not be a total
short circuit and the voltage applied during turns testing will not be
sufficient to bridge this partial short. However, during operation within
the finished product, the transformer is exposed to much higher voltages
which can cause a corona arc at the point of damage or the heating effect
of normal use may cause a short circuit after a short period of time.
By connecting a charged capacitor within the AT3600 to a
transformer winding, the winding is exposed to an impulse voltage and by
measuring the area under the decaying oscillation, it is possible to
establish if a breakdown between turns of the winding has occurred. The
diagram below illustrates the decaying oscillation of a transformer
winding with no insulation damage versus the same winding with damaged
Figure 9 Surge waveform examples
By computing the volt-second product under the curve, the
AT3600 provides a numeric quantity by which to establish good or bad
components. This gives the benefit of shorted turns detection using an
impulse voltage technique, while avoiding the potential errors inherent in
user interpretation of complex waveforms.
Figure 10 Example test entry screen for Surge Stress
using the Editor program.