A: On the anode foil of aluminum electrolytic capacitor,
an oxide film capable of withstanding the rated voltage even
if it is continuously applied at the maximum operating
In case when the voltage higher than the withstand voltage
of this oxide film (overvoltage) is applied, the anode foil
of aluminum electrolytic capacitor will form the
oxide film equivalent to the applied voltage.
Owing to the reaction, gases will be generated,
thus leading to the pressure buildup in the
capacitor. As the characteristics of capacitor, decrease
in electrostatic capacity and increase in tangent of loss
angle will be caused. The higher the applied voltage is
and the higher the ambient temperature is, the
more the gases are generated and the higher the
internal pressure. This may sometimes lead to the
phenomena such as swelling of sealing material
(rubber packing) and further to activation of safety
device (slipping out of rubber packing in the products with
no safety device). Therefore, avoid the use of capacitor in
the circuit where the voltage exceeding the rated
voltage may be applied to it.
The structural breakdown modes in case when overvoltage is applied are as follows:
The safety device is activated (or rubber packing slips out), and liquid
electrolyte in the capacitor is flown out, thus leading to dryup and
finally to open condition.
If the voltage higher than the withstand voltage of anode foil, that of
liquid electrolyte and that of separator paper is applied and it is no
longer possible to keep insulation, dielectric breakdown will be caused,
thus leading to short-circuiting.