On the problem of nondestructive diagnosis for quality assessment of electric insulation: A fractional calculus approach

Fractional calculus is used for theoretical description of a nondestructive diagnosis method for quality assessment of electric insulation in capacitors, transformers and other devices. The new analytical approach is based on deviation of the relaxation law from the exponential (Debye) one clearly observed in experiments on the long-time relaxation. Power modes of relaxation depends on charging prehistory and are sensitive to the state of an insulation system. As an example system, oil-paper insulation is considered. Fractional analysis of the measured polarization/depolarization currents is believed to provide indication of the general ageing status of the oil paper insulating system. Validity of the approach is confirmed by comparison of theoretical and experimental results for an oil paper capacitor.