Leakage inductance

[Edward Cain]

Hi Guys,
   Back in 1993 Bill KD0HG wrote a three part article, issues 50-52, in Electric Radio dealing with construction of a homebrew tube stereo amp. In that article he mentioned that Williamson specified that a successful output transformer should have a minimum primary inductance of 100 Hy's and a maximum primary to secondary leakage inductance of 50 mHy's.
   My question is how would one go about measuring leakage inductance?

Thanks in advance for any input.

Ed/KJ4JST

[W3GMS]

Hi Guys,
   Back in 1993 Bill KD0HG wrote a three part article, issues 50-52, in Electric Radio dealing with construction of a homebrew tube stereo amp. In that article he mentioned that Williamson specified that a successful output transformer should have a minimum primary inductance of 100 Hy's and a maximum primary to secondary leakage inductance of 50 mHy's.
   My question is how would one go about measuring leakage inductance?

Thanks in advance for any input.

Ed/KJ4JST

I have always done it by shorting the secondary winding.  Here is a link which describes the simple process:

http://www.home.agilent.com/agilent/editorial.jspx?cc=US&lc=eng&ckey=1356999&nid=-11143.0.00&id=1356999

Joe, W3GMS

[Edward Cain]

Thank You, Joe. So simple. I was expecting something complicated.

Ed

[W3GMS]

Your welcome Ed. 

I have done it many times since we use to design switching power supplies and the magnetics was a big part of that effort. 

Have fun!

Joe, GMS

[AB2EZ]

Ed

A minor comment:

Your original post asked about " ... primary to secondary leakage inductance..."

As a clarification, leakage inductance is associated with the sum of two effects:

The first effect is associated with the portion of the total magnetic flux, produced by current flowing through the primary winding, that passes through the primary winding, but does not also pass through the secondary winding. I.e. that portion of the total magnetic flux, produced by current flowing through the primary winding, "leaks" out of the core, and passes around the outside of the secondary winding (but does not pass through the inside of the secondary winding)


The second effect is associated with the portion of the total magnetic flux, produced by current flowing through the secondary winding, that passes through the secondary winding, but does not also pass through the primary winding. I.e. that portion of the total magnetic flux, produced by current flowing through the secondary winding,  "leaks" out of the core, and passes around the outside of the primary winding (but does not pass through the inside of the primary winding)


The leakage inductance of a real transformer (the sum of both of the above effects) is often represented by an inductor in series with the primary winding of an ideal transformer. In some cases (e.g. when individual winding capacitances and capacitive coupling between the windings have to be included in the model), the leakage inductance of a real transformer is more accurately modeled by an ideal transformer with an inductor in series with the primary winding, and another inductor in series with the secondary winding.

Stu