Measure leakage inductance of flyback transformer with multiple secondary windings

I have a transformer consisting of one primary winding and 3 secondary windings. Now I want to measure the leakage inductance at the primary side, so I need to short the secondary windings. Most of the literature I have read, there is only one secondary winding so it's pretty straightforward how to short the secondary side. But now, I have 3 windings at the secondary side, I am considering of 3 possible ways to measure the leakage inductance at the primary side: 1. Short 3 and 4, 5 and 6, 7 and 8 2. Short each winding one by one while leaving other windings open, e.g 3 and 4 shorted, 5 and 6 open, 7 and 8 open, etc. 3. Short 4 and 5, 6 and 7, 8 and 3.

Assume that my short circuit is perfect, what is the best method to measure? Thank you.

what is the best method to measure?

• Short the primary and test each secondary separately. The measured inductance (for each of the three tests) is the leakage inductance referred to the secondary.

• You could short each secondary and measure inductance at the primary but then you'd need to divide by the turns ratio squared to be able to place it in a model on the secondary side.

It all depends on what you are trying to achieve.

Regards actual measuring devices, you could use a meter that measures current and do some calculations to determine impedance and remove any DC resistance artefacts from the answers leaving you with inductance. Or, you could use an LCR meter operating at a frequency that is appropriate for the transformer type.

• Thanks for your answer. "Short the primary and test each secondary separately. The measured inductance (for each of the three tests) is the leakage inductance referred to the secondary." - I want to measure the leakage inductance existing at the primary side tho.... By the way, I have an LCR meter to use :) Commented Jan 30, 2020 at 9:18
• My bullet point 2 covers that but, it's all about what you are trying to achieve. I've given a couple of options (trying to scatter gun what you are trying to achieve) because, for instance, you might want to know individual secondary leakages on the basis that you want to understand regulation problems and how loading one secondary might affect the other. So, the best answer really depends on what you want the numbers for. Commented Jan 30, 2020 at 9:59
• Modeling a multi-winding transformer is a difficult exercise especially if you want to visualize the various winding currents in CCM or DCM. The best model I have ever found is the cantilever model described here:ecee.colorado.edu/~rwe/references/PESC98.pdf It properly accounts for the various leakage terms and, in particular, the inter-windings ones which are key to modeling coupled-winding regulation. Parameters extraction is long and tedious but simulation delivers amazingly-faithful results. Commented Jan 30, 2020 at 10:27
• @VerbalKint your link no longer works, but the doc can still be found by searching google for just PESC98.pdf. Also the title is "A Multiple-Winding Magnetics Model Having Directly Measurable Parameters". Commented Mar 22 at 8:21
• @gwideman, hello, thank you for these information on the broken link. I recommend another good seminar from CoPEC Cross Regulation Mechanisms in Multiple-Output Forward and Flyback Converters but I'm not sure about the Google link. It is a seminar Bob Erickson and Dragan Maksimovic taught a APEC in 1999. Commented Mar 22 at 8:44