Application of tuned sound enclosures to transformers

The objective of this program 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 mounted to a framework, that is, in turn, supported by the tank by means of mounting brackets and neoprene isolators. The development work was directed specifically toward application to existing transformers, i.e. retrofit.This project is a follow-on to work done under project RP-579-1. That project developed the theory and applied it experimentally to an existing transformer. The results were somewhat disappointing, however, with an 8 dBA reduction achieved where 15 dBA was expected. This document reports the work performed covering the period from March 1, 1977, to December 31, 1978. A complete noise shell enclosure was installed on a transformer for Consumers Power Company (Jackson, Michigan). Costs projected on the basis of this installation and several business assumptions indicate an installed cost of 19.8% of a new, standard noise transformer. This is higher than originally expected, but lower than alternative noise control methods. It also has some features that should make it an even more attractive alternative. Material loss factor (generally termed damping) of the enclosure material was found to be a critical parameter. Addition of a damping treatment to the experimental shell increased the performance to the 15 dBA target reduction. Damping was also found to be critical on the demonstration unit. The plastic panels installed (loss factor 0.05) resulted in a noise reduction of 8.5 dBA, increasing to 11.6 dBA when acoustical foam was added inside the enclosure. Three panels were replaced with damped steel panels and an overall 16.5 dBA reduction is anticipated based on vibration measurements