Threshold Current Density of Metallized Film Under Multiple Current Pulses

For metallized film capacitors (MFCs), the pulsed current would lead to the electrode fracture, the process might be accelerated under the repetitive pulsed current, and finally leading to the failure of MFCs. In order to study the mechanism of electrode fracture and its influencing factors, an experiment platform based on metallized film is established to observe electrode fracture by using a microscope. The experimental results show that for electrode fracture of metallized film, the threshold current density (TCD) is
$2.20 \times 10^{10}$
A/m
²
when the period is 310
$\mu \text{s}$
and the reverse factor is 10%. Theoretical results are also derived based on the analysis of electromagnetic force and Joule heat. The results indicate that, the fracture development is caused by the melting process of the electrode, together with the liquid metal flow driving by the electromagnetic force under the effect of multiple current pulses. Neither the electromagnetic force individually nor the direct vaporization would cause the fracture to develop. With respect to current distortion and heat conversion efficiency, the calculated peak current density is
$j_{\mathrm {max}} = 2.17 \times 10^{10}$
A/m
²
, which agrees with the TCD in the experiment. Thinner electrode has a larger TCD, when
$d_{m}$
decreases from 20 to 4 nm; TCD increases from
$1.07 \times 10^{10}$
to
$2.25 \times 10^{10}$
A/m
²
.