Purpose/Aim
Owing to the advantage of high reliability, metallized film capacitors are widely used in DC-link applications withstanding DC/AC superimposed voltage. Therefore, it is necessary to study the breakdown characteristics of metallized films under DC/AC superimposed voltage to evaluate the insulating properties of capacitors accurately.
Experimental/Modeling methods
Two overlapping metallized films are used to be the test sample. The DC/AC superimposed voltage with increasing amplitude is applied on the film until the film breaks down. An oscilloscope is used to record the voltage and current waveforms.
Results/discussion
The breakdown field strength of the metallized film hardly changes with k when the AC/DC voltage ratio k < 1, but decreases significantly with the increase of k when k > 1.The breakdown mainly occurs on the rising edge before the peak of AC voltage and keeps approaching the peak as k increases.
Conclusions
The main factor that causes the breakdown of the metallized film is the voltage peak rather than the voltage change rate. When the AC/DC voltage ratio is less than 1, the DC voltage can be used to evaluate the operating performance of the capacitor based on the peak equivalent principle.

Metallized film; DC-link capacitor; DC-AC composite voltage; breakdown