Space charge measurements in cables using the PEA method: signal data processing considerations

Fu, M., Chen, G., Davies, A.E. and Head, J. (2001) Space charge measurements in cables using the PEA method: signal data processing considerations. 7th International Conference on Solid Dielectrics, , Eindhoven, Netherlands. 24 - 28 Jun 2001. pp. 219-222 .

Abstract

The importance of space charge on the influence of the electrical performance of polymers has been the subject of numerous studies and several techniques of measuring space charge have been developed. One of the techniques is the pulsed electro-acoustic method (PEA) where acoustic waves are generated (by exciting any space charge present with an electrical pulse) which are measured using a piezoelectric transducer. To apply this technique to power cables, a curved transducer and absorber are often used which is problematic because of the difficulty of good acoustic contact between the transducer and the cable and between the transducer and the absorber. To overcome this problem, a flat ground electrode, transducer and absorber were employed in the new design. Another advantage of the new PEA system is its suitability for different sized cable. For the thick walled cable, the attenuation and dispersion of the acoustic wave during propagation through the insulation is no longer negligible. Care has to be taken with the interpretation of the output signal from the transducer as the divergent electric stress distribution as well as the divergent acoustic propagation can affect its magnitude. A data processing algorithm has been developed to obtain a true representation of space charge distribution across the cable insulation thickness. Using the modified PEA system and the data processing technique, space charge distributions under high voltage dc condition from two XLPE cable samples of different treatments have been presented in this paper. The results clearly demonstrate that the treatment has a profound effect on charge build up in the cable. Discussion of space charge effects on lifetime of the cable is also presented.

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