Vlf capacitor corona detection

Abstract

A method and apparatus for determining the presence of partial discharge ivity (corona) which makes use of corona current signals in the 20 MHz to 50 MHz frequency range and provides for identification of the corona source in a capacitor matrix. A current probe coupled to the high potential side of the capacitor detects corona discharge current signals that are fed to a bandpass filter which passes signals in the frequency range of 20 MHz to 50 MHz. The signals from the bandpass filter are amplified and integrated to provide a d.c. level proportional to the corona activity. The d.c. level signal is encoded by a voltage controlled oscillator and then converted to light. A fiber optic link transmits the converted signal to a remote console where the encoded light is reconverted to a d.c. level signal which can be displayed as an analog signal as well as activating an audio or visual alarm. A plurality of local current sensors and related circuitry corresponding to the number of capacitors in the capacitor matrix are provided to provide for comparisons of the corona signal levels from each capacitor to provide identification of the source capacitor containing the highest corona activity.