On the no-load loss of power transformers under voltages with sub-harmonics

Power transformers are traditionally designed for their utilization in sinusoidal voltage and current conditions. However, the non-linear loads are largely proliferated in the modern power systems. Thus, pec (point of common coupling) voltages and line currents usually have harmonically distorted or non-sinusoidal waveshapes. This study focuses on the parametrical analysis of transformer no-load loss under the excitation voltage with several sub-harmonic contents. For this aim, a computationally efficient technique is developed by combining both the harmonic-domain model of transformer windings and Finite Element Method (FEM) based modeling of transformer core. The obtained simulation results figured out that effect of sub-harmonic voltages on the transformer core loss is negligible. However, it is also seen that small amount of sub-harmonic voltages may highly contribute the winding loss under the no-load condition, and they should carefully be handled for the derating of power transformers.