TRANSFORMER TESTS VOLTECH AT3600 USER MANUAL
PAGE 7.1.50. VPN 98 - 024 TESTS AND TEST CONDITIONS
1.29. SURG - SURGE STRESS TEST
WHERE USED
This test may be used to highlight a short-circuit between adjacent turns in a winding.
It is applicable to any transformer, but is particularly suitable for transformers with a
large number of turns using very fine wire.
For such wire, the enamel coating is very thin, and there is a danger that it will be
scratched, giving rise to exposed copper. In some cases, the scratch does not
immediately cause a shorted turn, but will leave a weak spot which may eventually
fail.
By applying a higher than normal voltage across the winding, any weakness in wire
insulation will be encouraged to fail.
MEASUREMENT METHOD
Each SURG test can be programmed to consist of a number of impulses.
For each impulse, the AT3600 will charge an internal capacitor to the high voltage
specified. This stored charge will then be suddenly discharged into the winding-
under-test, and the resulting transient voltage will be analysed.
The product from the discharge will be a sinusoidal wave with decaying amplitude.
Where t
s
= The time of releasing the impulse
V
P
= The peak voltage just after switch-on
At the start of the surge test, the AT3600 performs an initial run to compensate for the
effect of the capacitance of the transformer winding. Without this compensation, the
peak voltage would be reduced by charge sharing between the winding capacitance
and the reservoir capacitance within the AT3600, and would not be the value you
require.
t
s
Time →
V
P
↑
Voltage
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