Accelerated capacitor degradation due to nonsinusoidal voltage supply and reliability of insulation systems

Reliability of capacitors for power factor compensation can be considerably affected by the quality of supply voltage. The presence of harmonic voltages and currents, in fact, can accelerate capacitor degradation to a significant extent, particularly when harmonic magnitudes are amplified by resonance conditions. The purpose of this paper is to infer self-healing capacitor reliability through life testing, modeling and failure rate evaluation. Statistical processing of life-test data shows that magnification of voltage peak due to harmonics is the main factor for ageing acceleration. A probabilistic life model is derived on the basis of this observation. The model enables failure rate, thus reliability, to be estimated for power capacitors. A working example shows how quantities useful for reliability inference in electrical plants, as MTTF, can be derived from the proposed model.