Experiences in applying specific sound power level based approach in electrical equipment

Two reasons for applying specific sound power level based approaches, in electrical equipment development process, are presented. The first reason is the comparison between fan alone performance and fan performance in the application. This also enables the comparison of the different cooling concepts and the comparison of the effects of design parameters (constructural measures) in a given cooling concept. The second reason is the applicability of the approach to the "risk analysis" or the estimation of noise emission of the product under development. In this paper the formulae on the following page are discussed. The formulae separate the noise generated and the effect of the noise control measures. The specific sound power level K is dependent on the fan and surrounding structures. The fan dependency can further be separated into fan (type) selection and constructural measures in it. The logarithmic terms in the equations are related to the aerodynamic and cooling performance of the system. DL describes the effects of noise control measures. These noise control measures can be divided into additional (e.g. noise kits) and structure dependent measures. It has to be noticed that in order to evaluate the insertion loss of the measures the effects on system resistance, out flow velocity (flow noise) has to be considered. In some cases additional noise control measures increase the K, usually due to chances in inflow conditions. It is also worth noticing that cooling structures can effect the flow rate (Q) and the effective system resistance "seen" by a given fan. Examples of this and the effect of the structure on DL are also discussed in the paper.