AT3600 User Manual

7.1.38 LVOC - Low Voltage Open Circuit

Where used

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 AT3600 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.

Measurement conditions

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:

The test conditions can also be determined automatically by the AT3600 according to this table:

Note that a ‘fixed’ voltage signal cannot be used with an ‘Auto’ frequency.