Mitigation Of Audible Sound In Power Transformers

Abstract

Transformer is the most vital equipment in a power transmission and distribution network, encompassing the entire network from generating station to user’s premises. During normal operation, it produces characteristic hum, the magnitude of which increases with increase in its capacity. This gets accentuated when added with the noise produced by the auxiliaries like cooling fans and pumps. 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 area-wise, 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. Hence the design and manufacture of transformer with low sound levels requires indepth understanding of the sources of sound and the possible remedial measures. The chief source of audible sound is the magnetic circuit of transformer which produces sound due to magnetostriction phenomenon, vibration of windings, tank and other structural parts, and the noise produced by cooling equipment. For the estimation of sound level produced by the transformer core, different empirical methods are used by the designers. However, for damping of sound transmission, multiple practices are adopted while manufacturing of transformer. Further, control of noise produced by the transformer auxiliaries is effected through judicious selection of oil pumps and cooling fans.This dissertation work focused briefly on understanding the genesis of sound generation, mode of sound transmission and detailed experimental investigations to establish effectiveness of various mitigation measures being adopted across the transformer industry. Recognizing the need for accurate estimation of transformer sound produced by the core right at the drawing board stage, the design of experiments, involving sound level measurements, was oriented towards study of the influence of various parameters, like flux density, methods of consolidation of core laminations, use of anti-vibration pads, use of sound absorbing panels, sound measurement profile etc. Results of there experiments are reported in the thesis and are summarized below. • Validation of empirical formulae being presently used. • Effectiveness of various sound mitigation measures like anti-vibration pads and sound absorbing panels.