An equivalent circuit for the leakage inductance of three-winding transformers is presented. The model is derived from the principle of duality (between electric and magnetic circuits) and matches terminal leakage inductance measurements. The circuit consists of a set of mutually coupled inductances and does not contain negative inductances. Each inductance can be computed from both: the geometrical information of the windings and from terminal leakage measurements taking two windings at a time. The new model is suitable for steady state, electromechanical transients and electromagnetic transient studies. The circuit can be assembled in any circuit simulation program such as EMTP, PSPICE, etc. programs using standard mutually coupled inductances.