Partial Discharge Characteristics of Low Kilovolt Class Capacitors

A set of advanced metallized polymer film capacitors was characterized as to their partial discharge (PD) behavior. The sample set of these capacitors was each at various stages of capacitor lifetime. The stages of lifetime were new/unused, moderate/midlife, and heavy use/end of life. The onset of partial discharges was initiated via the application of dc voltage not exceeding the design rating of 5 kVdc. The onset of PD´s in the polymer material was measured by a partial discharge analyzer (PDA). The PDA was capable of displaying the apparent charge of the PD´s down to less than 5 pC. Several of the capacitors under test exhibited characteristics of the phenomenon called graceful aging. Graceful aging being a process undertaken by dielectrics when the intrinsic defects already present within the material are cleared away by partial discharges. This process can reduce the original capacitance by up to a few percent. The loss of capacitance however was compensated for by the increased tolerance to a high electric field stress. This artificial aging by inducing partial discharges and characterizing the behavior may be of benefit to the capacitor industry as an accurate quality control to predict lifetime and performance of capacitors.