Pulsed Electrical Aging Tests of Insulation Systems and Components for Support of HV Power Supplies Design

Insulation of HV Power Supplies (HVPS) is exposed to a wide spectrum of voltage stresses, ranging from dc to pulsed voltages. The latter subject insulation to transients at amplitudes up to hundreds of kV at pulsed repetition rate (PRR) from fractions of Hz up to several kHz. It is argued that pulsed testing is appropriate for both pulsed and dc HVPS as limited by electrical aging. The ultimate goal is establishing design guidelines for adequate life for varied field configurations. Testing means comprise wide-band HVPSs and voltage dividers capable of voltage generation and measurement up to 210 kV. Life prediction is based on inverse power law with data mostly obtained in step-stress tests. Devices Under Test (DUT) varied from silicone potting samples with different field nonuniformity, to components, to complex insulation systems. For the first, an attempt is made to construct aging curves for equal life as a function of the field nonuniformity coefficient varied from ∼4 to ∼40 corresponding to rounded and needle electrodes, respectively. An exponent n=12 derived from step-stress tests was used in the curves’ generation. Capacitance loss and life of Polypropylene HV capacitors into billions of 10 kV-15 kV pulses is described. Lastly, aging and breakdown of transformer main insulation is studied with pulsed voltages up to 200 kV at PRR up to 60 Hz. One of the failure mechanisms was ascribed to partial discharges in the winding layer insulation. Although limited to electrical aging, pulsed testing can provide better guidance to design than both, or either, short-term and/or dc tests.