Control of transformer noise using an independent planar virtual sound barrier

A virtual sound barrier (VSB) can be applied to reduce transformer noise radiated outward from an
opening of an enclosure without scarifying natural ventilation and lighting. Although a traditional
independent VSB system consisting of multiple single channel active noise control systems has shown
practical potential for solving the noise problem of real transformers, the instability associated with the
system decentralization needs to be investigated. In this paper, a stability assessment method is proposed
for the independent VSB system consisting planar arrays of control loudspeakers and error microphones
first. Then the distance between the control loudspeaker and its collocated error microphone that is
required for stability is investigated based on the frequency characteristics of the noise and the Green’s
function in free field. Finally, the system stability and the noise reduction performance of a 44-channel
independent VSB system installed at the room opening of an onsite 110 kV transformer are presented.