Why Does Leakage Inductance Happen
Ideally, 100% of the energy in a transformer is magnetically coupled from the primary to the secondary windings. However, in reality, leakage inductance happens when some of the magnetic flux generated by the primary windings leaks and cannot pass through the secondary windings, thus reducing the signal induced in the secondary windings.
The level of leakage inductance is dependent on the good and bad design of a transformer, which has something to do with the physical separation between the windings, the spacing between the windings and the core, and the quality of the magnetic core.
This leakage inductance depends basically on:
- The winding geometry
- The core geometry
- Number of turns
The Effect of Leakage Inductance
You could think of leakage inductance as an extra inductor connected in series with an ideal transformer. It doesn’t take part in the energy transfer from primary to secondary but affects the performance of a transformer, such as voltage spike at the turn-off, voltage drop in the secondary, signal distortions, power losses
How to Minimize Leakage Inductance
When manufacturing transformers, engineers will take into consideration leakage inductance to make sure the transformer will function properly, by applying better winding methods, using good magnetic cores, and using insulation and shielding techniques.
- Decreasing the number of turns and layers
- Reducing the insulator layer thickness
- Using the interleaving arrangement
- Lowering the mean turn length
- Increasing the core window width
- Decreasing the core window height
In cases where higher leakage inductance is required, a magnetic shunt can be inserted between layers. Another possibility would be the use of fractional turns.