Insulation characterization with nonlinear impedance spectroscopy

Abstract:
A reliable characterization of the electrical properties of insulation is prerequisite for designing high-voltage electric power devices. Insulation with nonlinear electric behaviour represents a particular challenge. Modern (broadband) impedance spectroscopy equipment allows to measure at high AC voltages as well at small-signal amplitudes with super-imposed high DC voltage. In the first case, higher harmonics (“superharmonics”) can be measured, while the second case provides the differential impedance. This enables the investigation of nonlinear behaviour of material samples in an alternative way to measurements of polarization currents and DC current-voltage characteristics, and may yield additional information on the electrical properties. This contribution introduces briefly in the theoretical basics and illustrates the potential of the nonlinear impedance (or dielectric spectroscopy) with typical theoretical and experimental examples; particular focus lies on reconstructing nonlinear current-voltage characteristics.