Local heat source approximation technique for predicting temperature rise in power capacitors

A novel technique was proposed for evaluating a local heat source in film power capacitors by adopting a minimized analysis model. It is impossible to analyze directly the distributions of heat source in a capacitor element because of tiny scale of aluminum foil and polypropylene film compared to the length of capacitor element. To overcome such a multi-scale problem, here, we proposed a local heat source approximation technique (LHSA) by adopting the time-harmonic analysis of electroquasistatic (EQS) conduction law. To evaluate the dielectric losses in polypropylene film, the complex permittivity was introduced for calculating the effective conductivity subjected to the sinusoidal electric field. These numerical results show that the main heat source originated from the dielectric materials not the metal electrodes in film power capacitors. Finally, the computational fluid dynamic (CFD) solver was adopted by considering the conduction, natural convection, and thermal radiation effects. The results from the proposed method were compared to and were in good agreement with those from the experiments with five sample capacitors of 6600/3800 V, 60 Hz, and 100 kvar.