TRANSFORMER TESTS VOLTECH AT3600 USER MANUAL
PAGE 7.1.20. VPN 98 - 024 TESTS AND TEST CONDITIONS
1.11. TR - TURNS RATIO
WHERE USED
The AT3600 offer two basic alternative ways to confirm that the transformer has been
assembled properly, with the appropriate number of primary and secondary turns.
Turns ratio is the preferred test for signal, pulse and switched mode power
transformers, where the normal operating conditions require only small excursions of
the B-H curve, never extending beyond the linear regions.
(For line frequency transformers, designed to operate over the full extent of the B-H
curve, including the non-linear regions, the preferred method is to use an open -
circuit voltage test to check for the correct numbers of turns on each winding.)
Clearly a turns ratio test cannot tell you the actual number of turns on a winding, only
the ratio between one winding and the next. You should therefore have at least one
inductance test in your program to give confidence that the absolute number of turns
is correct as well as the ratio.
MEASUREMENT CONDITIONS
To measure turns ratio, a test source voltage is applied to one winding, the energised
winding, and the voltages across two other windings (one of which may also be the
energised winding) are measured using harmonic analysis. The turns ratio is
measured by dividing one measured voltage by the other, and making a compensation
for the effects of winding resistance.
It is recommended that you choose the winding with the highest number of turns as
the one to be energised. A possible exception to this rule is when you wish to
measure the ratio between two windings which should be accurately matched at 1:1.
In this case it may be better to energise a third winding with a lower number of turns,
to ensure that any measurement errors apply equally to the two windings under test.
You can specify the signal to be applied to the energised winding to have a frequency
in the range 20Hz to 1MHz, and an amplitude from 1mV to 5V.
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