Kiyoshi Wakimoto, Transformer Team, T&D Core Technology Development Office, Meidensha Corporation
Substations located near residential districts in urban areas are required to use low-noise transformers. Noise generated by iron core vibration (excitation noise) has taken into consideration such factors as reduction of iron core magnetic flux density, improvement of material properties, iron core structure (joints/clamps) and residual strain by machining as part of the efforts to move forward with noise reduction. When excitation noise becomes quieter, noise accompanying load current (load current noise) sometimes becomes an issue after having been ignored while excitation noise was being dealt with.
As part of initiatives for predicting load current noise or noise reduction, it was confirmed that results of modal analysis almost accorded with results of measurement by using a simple tank filled with water. By the same technique, the transformer tank of the product scale filled with insulating oil was modelled afterwards. And the vibration which spread in oil from windings to tank walls was calculated. Furthermore, JMAG was used in sound pressure analysis by the vibration of the tank filled with insulating oil. We will describe the examples of numerical analysis.