Corona discharge detecting apparatus including gatable amplifiers controlled by flip-flop means

Claim 1

Apparatus for detecting corona discharge in electrical inductive apparatus having a casing containing electrical windings disposed in a fluid, comprising: first and second mechanical to electrical transducers adapted to be disposed in vibration responsive association with the electrical inductive apparatus and provide first and second corona responsive signals, respectively, in response to a corona initiated sonic disturbance in the electrical apparatus, said first and second corona responsive signals each containing essentially the same common background noise, but different corona signals due to different locations of the first and second transducer means relative to the corona site, first and second amplifier means connected to said first and second transducer means, said first and second amplifier means being gatable between on and off conditions and providing first and second amplified corona responsive signals, flip-flop means for gating said first and second amplifier means to the on condition just prior to receiving corona initiated signals, first and second detector means connected to said first and second amplifier means, providing first and second unidirectional signals having a magnitude responsive to the first and second amplified corona responsive signals, a difference amplifier having output terminal means and first and second input terminals connected to said first and second detector means, respectively, said difference amplifier subtracting the first and second unidirectional signals and providing output signals at said output terminal means in which the noise common to both of said first and second unidirectional signals is eliminated, while the corona initiated portions of the first and second unidirectional signals are amplified.