2.36 LVOC - Low Voltage Open Circuit
The low voltage open circuit test is used to confirm that windings have
the correct ratio of turns between them, and that the phasing of the
windings is correct.
This test is used 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 region.
On the AT only, a high voltage open circuit test is available for testing
line frequency transformers at their operating point (up to 270V, 1kHz and
2A). See also the test TR - turns ratio.
To measure low voltage open circuit, the test signal is applied to one
winding called the energized winding.
The voltages across another winding (or the same, energized winding) is
measured. The low voltage open circuit measurement is the rms value of the
voltage measured and can be an ac or a dc voltage.
It is recommended that you choose the winding with the highest number of
turns as the one to be energised.
Choosing test conditions
The recommended test conditions depend on the inductance of the energised
winding; they are given in the table below assuming that the energised
winding is the one with the highest number of turns:
|Inductance of the
|Preferred test signal
|100nH → 1μH
1uH → 10μH
10uH → 100μH
100uH → 1mH
1mH → 10mH
10mH → 100mH
100mH → 1H
1H → 10H
10H → 100H
100H → 1kH
1kH → 10kH