To calculate the equivalent (leakage) inductance at 1000 Hz:
ù = 2ðf = 6.28 * 103
XLP = ùLP = 104
RP = a2RS = 11.7
Substituting in the given equations gives: XO = 1.3; and LE = 207 µH.
This (LE) plus the actual leakage inductance is the measured leakage inductance. For this example, the leakage inductance measures 360 µH (207 µH + 150 µH).
Now, calculating the equivalent inductance at 15,750 Hz:
ù = 2ðf = 9.89 * 104
XLP = ùLP = 1.63 * 103
RP = a2RS = 11.7
Substituting in the given equations results in: XO = 0.084, and LE = 0.85 µH. For all practical purposes, this (LE) plus the actual leakage inductance is the measured leakage inductance!
The table provides a listing of various transformers with their equivalent leakage inductance calculations at different frequencies and the leakage inductance measurements at f2. The measured inductance at f1 (LM1) for all tabulated transformers is within 20% of the calculation (LE1) when LL is subtracted.
A good rule of thumb when selecting the frequency for measuring leakage inductance is to be sure that the primary reactance (XLP) is at least 100 times the reflected secondary dc resistance (a2R).