Core microwaves generation may contain information on electric transformers aging

Abstract

This paper suggests that the presence of microwaves in high voltage transformers is caused by the creation of negative resistance associated with an internal parasite oscillator.Full performance of the electric transformer includes not only forced oscillations like the fundamental and its odd harmonics, assuming the input voltage sinusoidal and the nonlinear coil unpolarized. There also appear free oscillations. They have features associated with forced oscillations, so it might be better to characterize them as free-forced electric waves. We studied a circuit including a nonlinear core driving by two a-c waves designated fundamental and third harmonic. With the two input currents flowing through the coil, a complete set of modulation sidebands is generated.Our research suggests that wireless acquiring and further processing of these free microwaves may reveal new transformer features as aging.We review these concepts and offer some radiated microwaves measurements results taken below 115 KV industrial and dwelling electric lines circuits. Acquisition of microwaves is performed with a typical amplifier followed by a personal computer. Further, we realized a lab experiment with 16, 75 KVA distribution transformers looking for signatures related to forced aging. Transformers were conducted to failure by installing them in a high temperature camera. Measurements and processing of microwaves generation is a proposes a new way to assess electric power quality.