Accurate Estimation and mitigation of Audible Sound using Novel Technique of Flux Density Reduction at Design Stage in Transformer

Abstract

Transformer is the most vital equipment in transmission and distribution network, encompassing the entire network from generating station to user's premises. Till two decades ago, the sound produced by transformer was not attached any importance in public life. However, of late it is attracting attention as a result of the general public's growing concern about the environmental noise pollution. This is more so because, with the growing power demand, more number of power transformer are being installed in the close proximity of the populated rural, urban and suburban areas. In many countries, the local ordinances specify maximum allowable sound levels. As per Indian rules, there levels are specified areawise, viz. residential, industrial, commercial, and silence zone. Consequently, transformers with low sound levels are being increasingly specified by the users. For this reason, the sound level of transformer becomes an important consideration in design, manufacturing, installation and operation. During normal operation, it produces characteristic hum, the magnitude of which increases with increase in its capacity. The origin of the noise is the core vibration because of magnetostriction, which is a mechanical effect in core by the alternating flux. This paper presents the modification & validation of existing sound level calculation methods to estimate the accurate sound level at design stage, data of 26 Transformers was collected, ranging from 30 to 165 MVA rating. Existing method was modified by adding some factors. Also presents the outcomes of analytical study of sound level control technique, reduction of flux density by increasing yoke cross-sectional area of core through optimization using Memetic Algorithm. Optimum result was compared with Mgnetostatic analysis using Ansoft Maxwell 2D software.