Power transformer excitation force estimation for load noise reduction using experimental apparatus based on beamforming theory

To comply with noise regulations in residential areas, low-noise electrical transformers must be developed. However, it is difficult to accurately reflect the frequency characteristics of the transformer, which have a large influence on the noise produced, because the high voltage and current make it impossible to experimentally measure the internal excitation forces involved. In this paper, we propose a new method using an experimental apparatus for estimating the internal excitation forces experienced by transformers whose results accurately reflect the actual frequency characteristics of the transformer. To estimate the excitation force, the pressure distribution data outside the enclosure of a transformer was experimentally measured by the experimental apparatus based on a beamforming method, and the transfer function from the excitation source to the noise radiation was derived numerically. The excitation force was then derived using the pressure distribution data and transfer function. Based on the estimated excitation force, the contribution of each vibration transmission path was derived using transfer path analysis with integrated transfer function matrix as a basis for creating an effective noise reduction plan. The noise reduction plan based on our method was able to reduce transformer noise sufficiently to meet the noise standard set in standard transformer export contracts.