Parametric calculation of pulse transformer with open magnetic cores based on magnetostatic-field theory

Abstract

An analytical method for calculating the magnetostatic field of a pulse transformer with open magnetic cores is put forward in this paper, and formulas for calculating inductances of a small aspect-ratio transformer are derived. In comparison to results calculated by finite element magnetostatic-field simulations, the calculated values of inductance of primary winding L_{1} and the inductance of secondary winding L_{2} have a relative error of about 5%, while the error of the coupling coefficient (k) is less than 2%. Meanwhile, the effect of current nonuniformity in the primary winding on magnetizing inductance is studied. According to the calculated results, this effect reduces the magnetizing inductance and the coupling coefficient of the transformer, and can lead to an overvoltage phenomenon on the secondary winding. A small aspect-ratio pulse transformer with open magnetic cores is developed, which has a small size of 250 mm×150 mm in length and diameter, respectively. Inductances of the transformer are measured. The measured results conform to the law obtained in this work. Tests of the pulsed transformer are carried out. Experimental results show that the transformer can export a high-voltage pulse with an amplitude of 310 kV and full width at half maximum of 1 μs.