Transformer Noise Abatement Using Tuned Sound Enclosures. Final Report

摘要

The objective of this project was to reduce the noise emitted from power transformers by using a close-fitting, integrally-mounted noise shell. The noise shell consists of a series of panels attached to the tank by means of rubber isolators. Theoretically, this approach should yield noise reductions of 20 dBA or more. Sound absorptive materials are not required, and theoretical reductions in excess of that were achieved in laboratory models. The problem is, this technique is entirely theoretical and has not been applied to a practical situation. Accordingly, the overall objectives of this project were to test the noise shell theory and to adapt the theory to a practical application. The project was divided into two phases: development and commercial production design and demonstration. Transformer noise originates almost entirely in the core due to the magnetostrictive effects of steel, which cause the core to vibrate. Core vibrations are transmitted to the transformer walls, support members, radiators, and accessory equipment in two ways: through the core support structure and through the highly incompressible insulating oil. The most significant sound frequencies are in the lower region, between 120 and 600 Hz. Radiators are an important source of noise and must be treated to significantly reduce overall noise level. All sides of a transformer need to be enclosed including the reinforcing ribs. On pier-mounted transformers, the bottom is a significant source of noise and must be treated. A noise reduction of 8 dBA was achieved, compared to the target of 15 dBA. While somewhat lower than the goal, this work showed that the theory is adaptable to a practical application, and continued development is warranted. The deficiencies in theory were identified and corrective actions defined for future research efforts. (ERA citation 03:023683)