Normal Flux Distribution in a Three-Phase Transformer Core Under Sinusoidal and PWM Excitation

Transformer no-load loss and noise have been reduced considerably because of improved core material and improved core design. The variation of normal or interlaminar flux distribution (z direction) in a three-phase transformer core has been measured under pulse width modulation (PWM) excitation (no-load) with switching frequencies in the range of 1-3 kHz. The planar eddy current loss and attractive interlaminar force were analyzed for selected values of modulation index and magnetization condition (frequency 50 Hz; induction 1.5 T). Results showed significant reduction of the planar eddy current component and attractive interlaminar force for low modulation index with increasing switching frequency