VOLTECH AT3600 USER MANUAL TRANSFORMER TESTS
TESTS AND TEST CONDITIONS VPN 98 - 024 PAGE 7.1.29.
1.15. L2 – INDUCTANCE MATCH
WHERE USED
The inductance match test calculates the ratio between two inductances on two
windings. An equivalent series inductance measurement is performed on each
winding by measuring the complex impedance.
This test is suitable for switched mode power supply transformers, and audio &
telecommunication transformers. It checks matching between windings.
MEASUREMENT CONDITIONS
When calculating inductance match the tester performs two inductance
measurements. Firstly the unit applies an ac voltage across the first winding; it then
measures the voltage across and the current through the winding using harmonic
analysis. The measured voltage is divided by the current to obtain a complex
impedance and the inductance is calculated. This is then repeated for the second
winding. The inductance match is the ratio of first to second winding inductance.
The test signal can have a frequency in the range 20Hz to 1MHz, and an amplitude
from 1mV to 5V.
Generally, it is not necessary to measure the inductance at the normal operating
conditions of the transformer, which could involve, for example, voltage levels of
hundreds of volts. This is because the B-H curve can normally be assumed to be
linear in the operating region, and the inductance measured at a low level represents
the inductance that will appear in use.
Also, it can usually be assumed that the inductance value does not vary significantly
with frequency. Therefore, although high frequencies are available with the tester,
measurement frequencies above a few hundred kilohertz should be used with caution.
This is because the errors caused by the stray inductance and capacitance of your
fixture may become much more significant at these frequencies. Compensation can
be used to eliminate these errors.
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