Voltech AT360, User Manual

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7-39
For line frequency iron cored transformers where the inductance varies rapidly
with voltage a magnetizing current test (MAGI) is recommended. This test is
only available on the AT3600. See also the LS and LP tests for testing
transformers where a DC bias current is not required.
Test Conditions
To measure inductance with DC bias, the tester first applies and stabilises the
DC bias current and then applies an AC voltage across the selected winding.
The tester measures the voltage across, and the current through, the winding.
Using harmonic analysis, the measured voltage is divided by the current to
obtain the complex impedance from which the inductance is extracted.
Generally, it is not necessary to measure the inductance at the normal
operating conditions of the transformer, which could involve, for example,
hundreds of volts or several amps of bias. This is because the core material
can normally be assumed to behave linearly in the operating region, and the
inductance measured at a low level represents the inductance that will appear
in use.
Choosing Test Conditions
For optimum accuracy and performance, use the test conditions chosen for
inductance without bias in the previous section of this chapter.
The test conditions can also be determined automatically by the ATi according
to this table:
Signal
Specified voltage Specified current Auto Auto
Frequency
Specified Specified Specified Auto
Bias
Specified Specified Specified Specified
Note that a ‘fixed’ signal cannot be used with an ‘Auto’ frequency. The DC bias
current level must always be specified.