Influence of switching frequency on eddy-current losses in a three-phase, three-limb transformer core subjected to PWM voltage excitation

Transformers are key elements in power generation, transmission and distribution systems. Transformers under PWM supply are essential elements in industrial applications such as active power line conditioning, electrified railway power systems, PWM DC-DC power converters. Assessing the performance of transformers under PWM supplies is relevant to these applications. In this paper, the variation of iron losses with switching frequency in the range of 1 kHz - 3 kHz in a three-phase, three-limb transformer core under no-load conditions was measured. Classical eddy-current losses were calculated for various values of modulation index and magnetization conditions (frequency 50 Hz, 100 Hz; induction 1.3 T, 1.5 T). Results showed a reduction of the eddy-current component of loss by up to 40% at low frequency of magnetization and low modulation index with high switching frequency.