01_polazion_bd - Influence of polarisation on breakdown...

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Influence of polarisation on breakdown strength of polymeric composite dielectrics O.S.Gefle, S.M.Lebedev, YFPokholkov, D.FAgoris and I.Vitellas Abstract: The results of a study of electrical characteristics such as permittivity E, loss factor tan6 and breakdown strength E,, of new composite materials on the basis of polyvinylchloride filled with ferroelectric ceramic powder PZT are presented. It is shown that preliminary polarisation of composite materials by unipolar impulses of voltage enables the of composites to be increased by a factor of 1.3-1.5 in comparison with nonpolarised composites. It is discovered that the value of the specific accumulated energy may be increased up to lo5 J/m3. These composite materials can be used both for the electric field control in the insulation designs and for manufacture of capacitive stores of energy. 1 Introduction Composite dielectric materials (CDM) with suitable prop- erties are widely used in electrical engineering [ 1-51. However, a decrease in the dielectric strength caused by the difference in permittivities of polymeric matrix and filler does not enable us to reach a suitable specific accumulated energy for these CDM. This problem can be solved by performing a preliminary polarisation of CDM and improving the compatibility between polymeric matrix and filer. For example, as it has been shown in [6, 71, the dielec- tric strength of homogeneous dielectrics under impulse volt- age can be increased by a factor of 1.2-1.6 due to their polarisation under DC voltage at the same polarity as that of the impulse voltage. When DC polarising inhomogeneous dielectrics with sufficently high conductivity, an accumulation of space charge at the interface of polymeric matrix-filler occurs and it results in an increase in nonuniformity of the electric field distribution. The space charge accumulation should be excluded to study the influence of polarisation on the dielectric strength of CDM. It is possible if the polarisation time is very short. An alternative way of polarising CDM is to apply an electric field for a time comparable to, or shorter than, the relaxation time [2]. The main subject of this paper is to study the influence of previous polarisation on the dielectric strength under the impulse voltage. 2 Experimental procedure and samples A polyvinylchloride (PVC) compound filled with a ferro- electric ceramic powder PZT (lead zirconate titanate) with 0 IEE, 2001 IEE Proceehgs onhe no. 20010484 DOf 10.1049/ipsmt:20010484 Paper fmt received 18th December 2000 and in revised form 1st May 2001 OS. Gefle, S.M. Lebedev and Y.P. Pokhokov are with the Tomsk Polytechnic University, 2A, Lenin Street, 634034, Tomsk, Russia D.P. Agoris is with the University of Patras, GR 26500 Rion, Patras, Greece I. Vitellas is with the Testing Research & Standards Center, Public Power Cor- poration, 9, Leontariou Street, Kantza, 15351, Pallhi, Athens, Greece an average particle size of lpm was used as the sample material. The PVC matrix, consisting of a plasticised PVC resin and stabilisers was filled with PZT by using a labora- tory Banbury mixer. The ceramic powder of PZT was
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This note was uploaded on 06/11/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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01_polazion_bd - Influence of polarisation on breakdown...

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