3.4.8 LL or LLO - Leakage Inductance
The Leakage Inductance for a particular transformer is tested by measuring the inductance of a ‘primary’ winding when one or more ‘secondary’ windings have short-circuits applied.
Select either ‘LL Leakage Inductance’ or ‘LLO Leakage Inductance with Offset’ from the available tests window, to display one of the following form fill-in dialogue boxes as appropriate.
LL (Leakage Inductance) LLO (Leakage Inductance with Offset)
To program the test :
- Enter the signal and frequency required for the test.
Note that the signal is normally entered as a current by selecting the ‘uA’ or 'mA' button; but you may optionally enter it as a voltage by selecting the 'mV' button.
(Refer to Chapter 7 - ‘Test Conditions’, if you are unsure of the voltage and frequency to use.)
Note also that the Measure button may be used here as outlined in section 3.9, with the combinations of test parameter specification shown in the following table:
- 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.
- Select the high and low terminals of the coil to be energized (primary terminals). By clicking on the arrow to the right of the fill-in box, you will be provided with a choice of possible terminals. Double-click on the name of the required terminal.
- Select the secondary high and low terminals.
These terminals will be shorted out during the test. As the short-circuit applied via the relay matrix in the tester cannot be perfect, additional measurements will be made to these terminals to compensate.
- Select the additional low terminals.
These terminals are also shorted out during the test, but they are not used in the compensation measurements.
If only one secondary winding is to be shorted, then there will be no additional low terminals. If several windings are to be shorted, then the Secondary Terminals should be on the winding with the largest number of turns, and Additional Low terminals should be used for the rest.
- 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
||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.
- Select whether a user offset is required (LLO test only) and enter its value if applicable. This value will be added to the measured value to give the returned result.
Normally a user offset would not be required. However for small values of leakage inductance (<1μH) when there are a number of additional low terminals, it is not always possible during fixture compensation for the tester to remove all of the parasitic errors of the test fixture. In this case, the user offset may be required to fully remove the errors. The LLO test provides this additional feature.
- Select OK. The test specification will then be displayed in the program window.