Self-healing Behaviour as a Quality Standard

The capacitors manufactured by WIMA in winding technology are produced as single winding capacitors. The most effective pressure on the layers necessary for good self-healing behaviour can be individually adjusted for each capacitor.

WIMA capacitors are known for their excellent self-healing behaviour.

A DC voltage test is used to demonstrate the self-healing properties:

• the capacitor to be tested is connected over a series resistance of R ~ 10 k at with adjustable direct voltage source.
• the voltage on the capacitor is observed with a line recorder or an oscilloscope (see diagram).

• the voltage applied to the capacitor is continually increased, over and above the rated voltage for the capacitor, up to the first self-healing process. The line recorder shows clear breakdowns in the capacitor voltage and then recharging until the next self-healing occurs.

The voltage rate at the first breakdown and the number of self-healings which happen before the short-circuit finally occurs, allow definite conclusions to be drawn about the capacitor dimensioning or type.
This clearly shows that stacked MKT film capacitors short-circuit after a few self-healing processes. Also, the rate of the breakdown voltage is usually distinctly lower. A low loading capacity and a reduced life time are the result.

WIMA capacitors, on the other hand, are surprisingly hardy. As well as having very high breakdown voltage, they self-heal much more frequently than corresponding stacked film capacitors. The test clearly proves the high reliability and long life-span of WIMA MKS capacitors, well above the data given in the catalogue.