On the influence of core laminations upon power transformer noise

Power transformers can be sources of disturbing and annoying acoustic noise. This paper is a first phase report of a wider framework of study that investigates the noise radiation characteristics of air-cooled power transformers. The dynamics of the transformer core structure plays a significant role in the noise generation process. The reported work focuses on the influence of lamination of the core block on its structural dynamic behaviour. The degree of lamination of a core and its boundary conditions have been found to have a strong influence on its resonant behaviour and the need for an accurate modelling of these physical details has been observed through a combined experimental – numerical study. 1. Transformer noise – an annoying disturbance Power transformers are designed for the transmission and distribution of electrical power. Apart from satisfying this functional performance objective, the operation of a transformer happens to induce some annoying acoustic radiation. The requirement for more electrical power associated with the growing density of population, especially in urban areas, has resulted in enhancing the supply capacity of local electrical substations by adding more transformers, or building new substations of high power ratings closer to the neighbourhoods. This may result in the inhabitants in the vicinity being exposed to increased, and often disturbing, noise levels. Transformer acoustic noise is a hum characterised by spectral spikes at harmonics of the fundamental frequency (100 Hz /120 Hz) which is twice the line supply frequency. The transformer’s low frequency tonal noise components are the major source of annoyance and intrusion, invoking noise complaints from the residents, [1, 2]. A growing awareness and concern about public health problems due to noise pollution has brought transformer substations under the purview of tough regulations on excessive noise emission. Therefore, the need for compliance to stricter noise control regulations requires the construction of transformers that are less noise-prone and the design of efficient passive/active control systems for onsite noise control measures. For this purpose, a proper understanding of the noise generation in a transformer and an accurate estimation of its radiation characteristics are necessary.