Experimental comparison of localised magnetostriction difference under sinusoidal and PWM excitations

Abstract

The majority of power transformers are usually energized by sinusoidal excitation. However, there is a growing demand for using PWM excitation on power electronics devices for energy savings. As awareness of the environment also increases, the importance of noise and vibration issues becomes more significant. Increasing non-linear loads over time affect the ageing and lifetime of transformers. Such cases also cause to change the nominal values ​​of transformers. It is important that mechanical parameters such as vibration and noise can be accurately measured and examined so that all necessary functions can be entirely performed as other electromagnetic performances. For this reason, it is necessary to analyse the vibration movements of transformers and determine their characteristics, especially locally under changing operating conditions. Magnetostrictive is known as the main source of vibration and noiseof the transformer core. This paper presents localized magnetostriction of transformer core measured by strain gauges under sine and PWM voltage excitations. For validation of the study in this paper, a no-load strain measurement was performed experimentally on a real 20kVA three-phase three-limb T-joint transformer assembled in a laboratory.Localized magnetostriction in the rolling and transverse directions of the lamination under sinusoidal and PWM voltage excitations was carried out. The results of the experiment were compared with each other in terms of the location of the sensors.The Finite Element Analysis (FEA) was used to simulate the magnetic behavior of the transformer based on time-dependent analysis of magnetic field density, force, e.t. distributions under no-load conditions, respectively.In conclusion, evaluating the localized magnetostriction characteristic, especially under PWM voltage excitation, is essential for interlamination electromagnetic and electromechanical behaviors.