Open circuit voltage is measured by applying an ac test voltage to a selected winding (usually a primary winding), and measuring the resulting voltage produced on another winding.

You may program the test to use either the normal ac measurement, or a dc measurement, which could be used, for example, when testing transformers fitted with a rectifying diode.

If there are several windings to be tested, the program will execute more quickly if the following points are observed:

Place all the open circuit voltage (VOC) tests consecutively at the same point in the program.

Use the same energized winding, with the same test voltage and frequency for each test.

If there is a magnetizing current (MAGI) test which has the same energized winding and the same test voltage and frequency, place this immediately before the first open circuit voltage test.

On selecting ‘VOC Open Circuit Voltage’ from the available tests window, the following form-fill dialogue box will be displayed:

To program the test :

Enter the test voltage and test frequency.
Note that the Measure button cannot be used to determine any of the required test parameters.
Select either AC Voltage, DC Voltage or Mean sense, RMS scaled measurement by clicking on the relevant button.
Select (mouse click the button) the integration time you require.
'Medium' is the default setting. 'Long' will give more stable readings (for tighter limits) at the expense of an increased test time, and 'Short' will test at the maximum speed, but may give a slightly noisier reading.
Enter the terminal names for the Energized High and Low Terminals.
Click on the arrow to the right of the fill-in box, and you will be provided with a choice of available terminals; double-click on the one required.
Similarly, enter the names for the Measured Terminals.

Select (mouse click the button) the type of limits you require and enter the values.

%	Enter a nominal value and then the limits as negative and positive percentage values.
><	Enter minimum and maximum values.
>	Enter just a minimum value.
<	Enter just a maximum value.

Note that the Measure button may be used here as outlined in section 3.9.

Click on the appropriate button to choose the polarity, or choose the ‘No Test’ button. (For ac measurements, use the positive polarity when the measured winding has the same phase as the energized winding, use the negative polarity when they have opposite phases.)
Select OK. The test specification will then be displayed in the program window.

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