02_lifemodel_space - 514 Cauallini et al.: Life Model Based...

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514 Cauallini et al.: Life Model Based on Space-Charge Quantities for HVDC Polymeric Cables Life Model Based on Space-Charge Quantities for HVDC Polymeric Cables Subjected to Voltage-Polarity Inversions A. Cavallini, D. Fabiani, G. Mazzanti and G. C. Montanari DIE-LIMAT, University of Bologna, Wale Risorgimento 2 40136 Bologna, Italy ABSTRACT This paper illustrates a new model that enables the estimation of life of polymeric insulation subjected to dc stress, both in the presence and in the absence of voltage polarity inversions. The derivation of the model parameters is based on the results of space charge measurements and accelerated life tests realized at constant dc stress, which allows the characterization of the performance of insulating materi- als under dc electrical stress to he carried nut in short times. The expected life of a cable in service can be evaluated by means of this model, provided that the rate of voltage inversions expected during its life is known or estimated. The model is ap- plied here to results of tests carried out on polyethylene-based materials for cable insulation, and model parameters are calculated resorting to two different ap- proaches. A satisfactory fitting of life test results is achieved, thus confirming the ialidity of the proposed model. 1 INTRODUCTION ILE polymeric cables are replacing ac impreg- are still affecting the development of polymer-insulated cables for HMC application. Indeed, polymeric insula- tion commonly used for ac cables, i.e. cross-linked polyethylene (XLPE), may not endure dc stress, particu- larly in the presence of voltage polarity inversions that are likely to occur in dc lines for energy-flow dispatching. This is pushing researchers towards the study of new polymeric materials, essentially polyethylene-based, but containing additives or blends. The characterization of the performance of polymeric insulating materials under dc voltage is generally achieved resorting to space charge measurements [l-51, but even if there is no doubt about the significant role played by space charge on insulation performance, the analytical relation- ship between space-charge associated quantities and life in the presence and in the absence of voltage polarity in- versions is not yet known. However, a clear correlation between stored space charge, maximum internal field, rate of space charge depletion and ratio between life with and without inversions is shown in [6], while a phenomenologi- cal approach to life modeling under dc stress is discussed in [71. This work presents a new model that provides life esti- mation of polymeric insulation subjected to dc stress, with w nated-paper cables worldwide, significant problems Monuscnpl receiued on 5 October 2001, in find form 7 May 2002.
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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02_lifemodel_space - 514 Cauallini et al.: Life Model Based...

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