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Non-destructive screening method for film capacitors

IP.com Disclosure Number: IPCOM000240788D
Publication Date: 2015-Mar-02
Document File: 5 page(s) / 118K

Publishing Venue

The IP.com Prior Art Database

Related People

Elena Mengotti: AUTHOR

Abstract

Dissipation Factor (DF) measurements aim at the inefficiency of the insulating material under testing. With DF the heat that is lost dielectric loss) when an insulator is exposed to an alternating field of electricity is measured. For capacitors the main source of dielectric loss are partial discharges (PD). Specifically, for multilayers capacitors, partial discharges in voids are enhanced at high frequency, due to the fact that at high frequency the time for charge decay is reduced, together with the breakdown voltages reduction of the media. These characteristics are the principle used behind this disclosure to differentiate among good and bad MKPs. By measuring the DF at high frequency, partial discharges at defects which are less vulnerable are provoked and detected. From the difference in DF reading, “defect condition” in specific capacitors is revealed and robust units can be identified among the same produced batch. Namely, long life capacitors will have a lower dissipation factor at high frequency than capacitors which have more defects.

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Non-destructive screening method for film capacitors

Author: E. Mengotti

TECHNICAL FIELD

The present disclosure describes a testing method for film capacitors involving high frequency measurements. The method proposed is able to compare end-of-life behaviour of plastic encapsulated capacitors without reducing the lifetime of a good device. The advantage of the idea is a fast, cheap and non-destructive methodology which allows for an effective reliability evaluation of a batch of identical capacitors.

BACKGROUND OF THE DISCLOSURE

Many power electronic systems are used in applications where maintenance and repair are difficult, costly, or impossible. Metallized film capacitors (MKPs) are one of the most used capacitors in power systems due to the small sizes, low losses and cheap price. By tackling reliability failures during the whole lifetime of these capacitor components (infant mortality, random failure regime and end of life), the total reliability of many power systems will be improved significantly. Burn-in testing is usually used to eliminate infant mortality failures in many electronic components or systems: The drawback of this test is that good units' lifetimes is reduced during the testing time and this is an inevitable consequence.

In this disclosure, a simple, economic non-destructive alternative to burn-in for MKP is disclosed to reveal whether inside a batch of MKPs which ones will have a longer or shorter life. The defect free status of MKPs can be assessed before assembly process of the component into a more complex system.

The problem to be solved is to find a screening method that affirms the long term reliability of metallized film capacitors without consuming lifetime of good component. The method should therefore sort out all those components which are prone to early failure by not aging all other components. The screening testing method should be therefore non-destructive (NDT). To be applicable in production, it should also be an efficient method, meaning that a larger quantity of "bad" samples can be screened by the testing.

In conclusion, the goal is a replacement of the "burn-in" method providing several benefits compared to the existing burn-in method i.e.:

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 27.02.2015 CH-1420301

• non destructive

• not aiming only at infant mortality cases (which are general fabrication defects) but aiming at the long term life time

Many testing and screening technologies for capacitors are already existing and protected with IP. Among these testing technology several focus on defect screening for multilayer caps. The screening method existing are focusing on various measurements value of the capacitors such as: insulation resistance, charging and discharging capability, AC behavior among others. No method has been found having a non-destructive character. Moreover, no method has been found that is focusing on the dissipation factor measurement at higher frequency.

SUMMARY

Di...