Capacitive behavior of HF power transformers: Global approach to draw robust equivalent circuits and experimental characterization

This paper addresses the representation and the characterization of the electrostatic behavior of n-windings HF power transformers. A global approach, mainly based on energy considerations about linear electrostatic circuits, is introduced. It leads to equivalent circuits which include minimum numbers of elements. Besides, owing to a special approximation that is often acceptable, the general circuit can be greatly simplified and so it is for the experimental identification. This is discussed. Then, knowing the topology of the needed circuits, we show how to experimentally find the values of all involved components. This is achieved by using a wide frequency range impedance analyzer according to a well defined process. An industrial 3-winding transformer is used to illustrate this identification process and, finally, curves related to the equivalent circuit are compared to experimental ones.