In this paper，a simple and practical determination method for optimal acoustic noise levels of transformers to be upgraded in an aged outdoor substation is proposed. The solution is based on the Linear Programming using an empirical formula for estimating noise levels at the boundary points around the substation premises. Input parameters necessary for the developed algorithm are three dimensions of each transformer and distance between transformers and each boundary point. Constraints are derived from the empirical formula 　 for estimation of noise level at the boundary points，which takes into account the decay effect by distance，and the regulated noise levels on the boundary. An equivalent sum of transformer noise levels is chosen as an objective function to be maximized. The Proposed approach was successfully tested on a model substation (2 banks) and a real primary substation (5 banks)to show its validity and practicality.

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