New concept of active control of transformer noise, Part 1: The active envelope

A new concept of active noise control for transformer using a set of independent control units distributed on the transformer blade has been proposed. A theoretical model has been developed to determine the optimum distribution of the control unit on a transformer surface. An experimental setup composed of 24 control units has also been realized. This system allowed to determine that a distance of about 0.20 m between the error sensor and the speaker of each control unit ensures good stability of the system. An experiment realized on a real transformer gave a noise reduction of 10 dB of the first harmonics.