Load Noise Prediction of High-Voltage Transformers by Equation Applying 3-D EMCN

Abstract

This paper proposes a method for predicting the load noise of high-voltage (HV) transformers. When the transformer is loaded, the electromagnetic force is generated by the interaction between electric and magnetic fields. This force, the so-called Lorentz force, induces the vibration of the winding structure causing the load noise of transformer. Therefore, calculating the Lorentz force plays a crucial role in predicting the load noise. Herein, a 3-Dimensional equivalent magnetic circuit network (3-D EMCN) is applied to calculate the Lorentz force, instead of 3-Dimensional finite element analysis (3-D FEA) to shorten the computation time. Subsequently, considering the relationship between the sound pressure and the Lorentz force, the calculated force can be applied in the equation for the sound pressure level (SPL), which represents the relative sound pressure on a logarithmic scale. The formula for the sound pressure varies depending on the sound source model. The source model of load noise can be represented as a dipole source because the structure of the transformer windings is considered as an unbaffled speaker. The transformer parameters identified to affect the load noise are additionally considered for more accurate prediction of load noise. The parameters identified to increase the load noise are simply multiplied to the equation, whereas those with the opposite effect are multiplied inversely. Finally, after this compensation process, the accuracy of the load noise prediction equation is calculated as the standard deviation of the differences between the experimental and calculated results.