Leakage impedance design as function of frequency scaling in power transformers

Abstract

The paper describes the relationships that exist for leakage impedance as function of frequency scaling a power transformer by either adjusting its size or by adjusting the number of cores in a distributed transformer. The frequency dependency of losses in ferrite materials are also taken into account. It is demonstrated that the leakage inductance of a lumped transformer is generally larger than that of a comparable distributed transformer. At high power levels and frequencies, it is beneficial in terms of power density and cooling to subdivide a transformer into smaller transformers. A new approach to achieving high leakage inductance in a distributed assembly is introduced. Finally, a case study of two 70 kHz stacked core transformers with high leakage inductance, for application in a 40 kW plasma burner, is presented.