Voltech AT5600 User Manual page 141

C H A P T E R 7 – T E S T S
Transient Analysis
During the decay phase after the impulse has been fired, the AT5600 measures
both the voltage amplitude along the transient, and the time of decay.
The AC waveform (and frequency/amplitude/decay rate) is a function of the
characteristics of your UUT and the AT5600 Capacitors used to discharge the DC
spike.
A good transformer will have a clean and sustained transient, with a long decay
period. A transformer with a shorted turn will have a heavily damped response,
with a shorter decay period.
The calculation performed is to calculate the 'area' underneath the graphical plot
of the decaying transient. (For the calculation used, both negative peaks and
positive peaks add to the total area.) The area, measured in Volts-seconds, is
much smaller for the faulty winding with a shorted turn.
Specifying the Test Limits
It is very difficult to predict the Volts-seconds 'area' under the curve from
theoretical calculations, so the limits should be calculated from measurements
taken from a known good part. The recommended method is to use the Measure
Mode (see section 14.6.26) to obtain some values.
The procedure is as follows:
1. Measure the area on a known good transformer; let this result be area A
2. Wrap an additional single turn around the core, short the two ends together,
and re-measure the surge; let this result be area A
3. Set the limits as follows:
4. Max Area = 3A
5. Min Area = (A
Because these limits are taken from only one transformer, they may need to be
revised after more have been tested.
AT5600 User Manual 98-119 issue 14
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