Barnett, M; Morrell, R; Hill, G J; Cain, M G (2000) EC SMT project, 'CERAMELEC' WP10 - Electric Strength. NPL Report. CMMT(A)294

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Abstract

This report covers the activities within WPI0, which had the objective of reviewing electric strength tests for modem ceramic materials. The background to undertaking the work is described, together with the experimental approach employed. Using an alumina substrate product and two PZT piezoelectric materials, various factors associated with the geometry and production method for the specimen were investigated. Statistical evaluation of breakdown data using the well-known Weibull distribution was made to establish the usability of the method for electric strength. The following conclusions have been reached.
- Thin planar test-pieces ranging in thickness between 1.0 and 0.25 mm and with electric strengths exceeding 100 kV/mm can be electroded and tested without difficulties of edge racking or flashover when tested in transformer oil;
- Differences in electric strength can be systematically resolved using sufficient test-pieces, and examples have been obtained indicating electrode area effects, thickness effects, and machining/annealing effects;
- Dimpling test-pieces is unnecessary to prevent edge flashover; producing small dimples in thin test-pieces is not a simple task and requires specialised precision equipment;
- Test results from nominally identical samples have been found to possess a variation in electric strength which is expressible in terms of the two-parameter Weibull distribution;
- The quality of thin evaporated electrodes must be such that breakdown positions areuniformly distributed over the surface of the electrode;
- Concerns that breakdowns will occur preferentially around the periphery of the electrodes in planar test-pieces as a result of electric stress concentrations have proved to be unfounded.
For testing advanced ceramic products, it is possible to devise a suitable standard with greater flexibility than the existing method given in IEC 60672-2 for traditional ceramics. A draft standard will be submitted to CENELEC.
Areas that have been identified for further work include needs for quantification of the quality of applied electrodes and of the role of electrode area, and for identification of whether the Weibull distribution concept can be extended to electric withstand tests.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	CMMT(A)294
Subjects:	Advanced Materials Advanced Materials > Powder Route Materials
Last Modified:	02 Feb 2018 13:17
URI:	http://eprintspublications.npl.co.uk/id/eprint/1632

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