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The research has investigated the development of improved dielectrics by optimising all aspects of the manufacturing process including:
polymer resin type, purity and additives;
film extrusion, orientation and morphology;
capacitor winding, impregnation and heat treatment;
criteria for customer acceptance.

Research has been carried out in order to optimize the processing of polymeric film dielectric to obtain a significant improvement in the performance of alternating current (AC) power capacitors and has involved materials producers, capacitor manufacturers and end users. The methodology involves the manufacture of resin and biaxially oriented polypropylene (BOPP) film over a wide range of conditions followed by the evaluation of these products in experimental capacitors. It is shown that the presence of electroactive components in the polymer can influence performance and a new technique for determining this factor in resins and films was devised. Large numbers of capacitors were tested and by a procedure of design and materials selection compliance was achieved with a target specification.

The main results from the work are as follows:
establishment of a clear relationship between the electrical performance of capacitors and electroactivity in the polymeric materials from which they are fabricated;
establishment of an important test procedure to determine the extent of electroactivity in resins, films and solvent extracts;
improvement of the low temperature and transient overvoltage (TOV) performance of capacitors by design factors including the use of laser cut foil electrodes;
improvement of the high temperature performance of capacitor by materials selection and purification;
development of a diagnostic routine to measure degradation in aged dielectric;
successful testing of capacitors at the target operating stress of 75 V(rms)um{-1} (average) giving a significant improvement in volume efficiency with corresponding reductions in physical size and material content.
This coordinated activity covers the development of improved dielectrics with optimisation of conditions across the whole manufacturing process to include:

-polymer resin type, purity and additives;
-film extrusion, orientation and morphology;
-capacitor winding, impregnation and heat-treatment;
-criteria for customer acceptance.

The coordination of work involving manufacturing and interactive processes carried out by different manufacturers is a key element in achieving the rapid development of materials, enabling the production of power capacitors with increased operating stress, improved reliability and increased temperature range.


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Cleeve Road
KT22 7SA Leatherhead, Surrey
United Kingdom

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