Click the calculator icon 
to enter the custom parameter value. The 
icon indicates that the automatically generated ETS parameter is changed by user.
Click OK to close the dialog box..
The Requirements and Test form displays and allows you to edit the electrical specifications for the transformer used by PI Expert when creating and documenting the design.
To edit the automatically generated parameters:
Click the calculator icon to enter the custom parameter value. The icon indicates that the automatically generated ETS parameter is changed by user.
Click OK to close the dialog box..
The changed condition or specification will be highlighted and used in the documentation of the transformer. You can also change the default Electrical Strength using the Preferences dialog, Transformer Defaults tab.
Leakage inductance results from imperfect magnetic coupling of the primary and secondary windings. Leakage inductance can be defined as any magnetic flux that does not link the primary winding to the secondary windings. Thus, it acts as series impedance with the primary winding. Leakage inductance is undesired in switch mode power supplies and should be minimized through transformer construction and PCB layout.
Magnetic flux lines flow as a result of current flowing through the primary winding. This flux links through the magnetic circuit (that is the core) to the secondary inducing a voltage across the secondary winding. There is some flux that does not link to the secondary which gives rise to leakage inductance. Leakage inductance is undesired in a switching power supply, but it is something that cannot be completely eliminated. It is a function of the physical distance between the primary and secondary windings.
The software calculates a crude maximum tolerance for this leakage inductance based on device family and power level, as a guideline specification for the transformer manufacturer.
It is especially important to minimize leakage in higher power designs as this may result in large voltage spikes at switching transitions. To minimize leakage inductance, it is recommended to use the split primary construction technique for higher power designs.