Derating of Anisotropic Transformers under Nonsinusoidal Operating Conditions

Abstract An iterative algorithm is developed for the computation of transformer derating factors (functions) under (non)sinusoidal excitation and linear (R, RL, RC) loads. The proposed nonlinear model is a combination of frequency domain (to incorporate harmonics) and time domain (to account for saturation) techniques and only requires transformer parameters and λ–i characteristics. The derating factors are generated using the computed transformer apparent powers under ‘rated losses’ and ‘rated fundamental output voltage’ conditions. Computed voltage and current waveforms and total losses are compared with measurements and show good agreements.