Utilisation of voltage and frequency dependence of stress-grading materials in dielectric diagnostics [electrical insulation]

Diagnostics of electrical insulation is increasingly performed with the frequency and amplitude of the applied voltage varied over wide ranges. Cable terminations and high-voltage machine end-windings have stress grading systems whose response alters measured capacitance and loss components even in measurements at power frequency. Non-linear stress grading materials also contribute harmonic currents to the measured response. Excitation at frequencies other than power frequency changes the grading´s potential-distribution, affecting the measured capacitance and possibly inciting partial discharges that contribute to measured loss and harmonic currents. Understanding of the effects of such stress grading systems is important for analysis and possible compensation of dielectric measurement data.