Identification of SOZ and Influence on Neutral Current and Flux Distribution Capability in a Y-y Power Transformer Subjected to DC Bias

In line with the advancement in technology there is an extensive use of power electronics in the power systems as the demand for more efficient and smart energy grows. The widespread use of power electronics in power transformers can introduce dc bias into the system, causing it to change operating point, generate harmonics and increase excitation current. In this work we have modeled a Y-y type 11kV/433V natural air-cooled power transformer using Ansys Maxwell software. This model has been analyzed using the finite element method. A comprehensive analysis of the flux distribution capability and the influence on the neutral current in a dc biased transformer was performed. This study provides new insights into various zones of operation of the dc biased transformer. The resulting nonlinearity of operation with increasing dc bias could lead in leakage flux, neutral current, and losses, causing a lower lifetime expectancy and poor power quality over time. Collectively, our analysis demonstrates that identifying different operating zones and operating the transformer in the safe operating zone (SOZ) can extend the life of a transformer while also providing significant safety and reliability benefits.