Sound power level determination for large steam turbine generators

A technique is presented for calculating the approximate total sound power level (PWL) of large steam turbine-generators as well as the PWL of individual turbine-generator components. A near field approximation is used which is similar in structure to the new IEEE test code 85. Modifications are introduced in the test code procedure to reduce the effect of component flanking noise, and noise contributed by extraneous sources. The overall turbine room PWL is also calculated by a reverberant field technique and compared to PWL as calculated by free field methods. Measurements were made around ten large steam turbine generator units ranging in name plate rating from 390 to 1050 MVA. PWL´s of turbine-generators were found to increase by approximately 3.5db for each doubling of unit rated MVA. PWL´s calculated from indoor near field approximation show a 3 dbA increase over PWL´s of outdoor units of equivalent rating. This difference is an indication of the need for further development of methods for determining sound power level.