- How is SURG measured?
- Is it possible to get different SURG results for different revisions of the AT3600?
The purpose of this test is to detect an inter-turn short by applying a number of high voltage impulses (or surges) to the selected winding. Each impulse produces a sinusoidal transient, which eventually decays to zero.
During the test, the tester measures the area (in Volt - seconds) under each transient. The decay is much shorter in a faulty winding, and is detected as a smaller value for the measured area.
Cautions for measurement.
The surge test charges a capacitor. Then the capacitor is discharged into the transformer winding.
The result of the SURG test depends on the value of C in uF, the ac impedance of the winding, the impedance of the connections and of course the voltage.
1. In some old issue AT3600 the value of C was different, so the result will be different. This applies to testers manufactured before 1999.
Please contact us if this is the case and your AT3600 has not been serviced by Voltech recently.
2. The connection impedance can be very important because large currents can flow. If the fixture does not have low impedance connections and the fixture contact resistance is not repeatable, different results can be measured over time.
3. Small differences in the transformer L or Q can change the SURG result.
For the same type of AT3600, with the same good fixture and the same test part, results will be very similar.
SURGE is not an absolute test, but is best used to check conformity by setting the target result based on a sample of known good transformers.
Is it possible to get different SURGE results for different revisions of the AT3600?
Neither the old PWR card or the new PWR card can be said to give 'wrong' readings, but it may be confusing for customers who have several units with different hardware build revisions and the vale of the C SURGEcapacitor maybe different.
Why the Value of C or L changes the SURGE result.
The following formula defines the resonant frequency of the components associated with a SURGE Test.
Freq = 1 / ( 2 * pi * sqrt (L * C ) )
On the old power board C = 3.3 nF
On the new power board C = 3.0 nF
It can be seen that this capacitor will change the resonant frequency, this causes the resonant frequency to change.
Hence SURGE test results may change from older to newer AT3600 products.