Development of a Low Noise FOA Transformer Cooler Part II: Acoustic Design

The design of the acoustic treatment for a new, modular, low noise, forced oil and air (FOA) transformer cooler that can be used with new and existing transformers is described in this paper. Air is moved vertically through the cooler with asymmetric airfoil bladed fans located at the vertical center and the heat exchangers and acoustic mufflers are located symmetrically above and below the fans. The design goal was to reduce cooler sound emissions to below 57 dBA measured at a distance of 6 feet (1.83 m) while dissipating 200 kW and 47 dBA at 100 kW heat dissipation. Cooler dimensions were constrained to a 5 foot by 7 foot (1.52 m by 2.13 m) base area and a 25 foot (7.62 m) height. Noise abatement was achieved by using parallel baffle dissipative mufflers and glass fiber lined air inlets and outlets. The acoustic components were designed using an iterative process to maximize the attenuation while minimizing the pressure drop through the cooler. The fan and heat exchanger design is discussed in Part I of this paper.