3.4.11 TRL - Turns Ratio By Inductance
The TRL test measures the turns ratio between a pair of windings by comparing their inductance. This is different from the TR test, which compares the voltage used to energize one winding, with the voltage induced on a second. The TRL test is preferable to the TR test when the coupling between the primary and secondary windings is poor.
An alternating voltage is applied to each winding in turn. The alternating currents that flow and the applied voltage at the transformer are measured. From these measured currents and voltages a complex-impedance is derived, and the inductance is then calculated. The turns ratio is computed by dividing the square root of the primary inductance by the square root of the secondary inductance.
On selecting ‘TRL Turns Ratio (from inductance)’ from the available tests window, a dialogue box will be displayed.
To program the test :
- In the fields provided, insert the voltage and frequency you require for the test (see chapter 7 - ‘Test Conditions’).
Note also that the Measure button may be used here as outlined in section 3.9 of this chapter, 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 primary winding. (Click on the arrow to the right of the fill-in box and you will be provided with a choice of the available terminals. Click the required terminal.)
Select the high and low terminals of the secondary winding.
- Select (mouse click the button) Ratio (%), or Turns (#) limits.
Enter the required limits:
Enter the nominal Primary to Secondary ratio, together with the limits as positive and negative percentage values.
In turns mode you may set upper and lower limits on the primary and secondary windings. The transformer tester will then set limits on the turns ratio which are equal to the sum of these two errors, e.g.:
the tester will set the following limits on the ratio:
||± 2 turns
||± 2 turns
upper limit = 104/100 lower limit = 96/100.
If you wish to set limits on only one winding, you must enter zero (0) as the limit for the other winding.
Note that the Measure button may be used here as outlined in section 3.9.
- If required, the polarity of the test can be checked. Click on the expected polarity of the transformer turns, otherwise disable the test by selecting ‘No Test’.
- Select OK. The test specification will be displayed in the program window on the screen.