Core monitor that uses rotor shaft voltages

摘要

The present invention is a monitor that detects generator core 12 hot spots where the insulation between ferromagnetic sheets is breaking down by monitoring rotor 10 shaft voltage. The difference between the differential shaft voltage at each end of the rotor 14 produces a voltage signal that changes as the core 12 malfunctions. By comparing signal samples over time, core failure can be detected. Spring loaded rotor shaft brushes 20 and 22 connected to differential isolation amplifiers 24 and 26 obtain the voltage between ends 16 and 18 of the rotating shaft and nearby frame, and a differential amplifier 28 produces the difference between the shaft end differential voltages which is the shaft dissymmetry voltage. An analog-to-digital converter 30 produces digital values of the dissymmetry voltage which can be converted into a voltage frequency spectrum by a Fourier Transform routine executed by a computer 32 or analyzed directly. The computer 32 monitors the spectrum or time domain signal over time for changes and produces an alarm when the changes exceed a threshold. Bandpass filters 34 and a simple threshold comparison routine or analog threshold devices can substitute for the FFT routine.