The role of trapped space charges in the electrical aging of insulating materials

An investigation of the effect of trapped space charges on the aging of polymeric insulating materials subjected to thermo-electrical stress is reported in this paper. Possible scenarios of degradation mechanisms, thermally activated, but accelerated by the presence of space charges, are examined. The model which derives from this approach has some interesting features: it is characterized by electrical and thermal thresholds, its parameters have a physical background, it can be cast into a probabilistic framework. Acceleration of aging due to space charges is attributed to a reduction of the free-energy barrier to degradation, seen as a local partially-reversible reaction, which is caused by energy stored in space-charge centers. The validity of the model is limited to dc voltage, and to the time of formation of microcavity-crazes, rather than to breakdown times, since other mechanisms will occur under electrical field once large enough cavities are formed in the insulation. The model is applied to the results of thermo-electrical life tests performed on PET, showing very good fitting, as well as interesting relationships between parameter estimates and insulation morphology. It is shown that the model can also fit well to ac life data, where it takes on a phenomenological meaning.

[1]  G. C. Montanari,et al.  A Probabilistic Insulation Life Model for Combined Thermal-Electrical Srresses , 1985, IEEE Transactions on Electrical Insulation.

[2]  L. Simoni,et al.  A General Approach to the Endurance of Electrical Insulation under Temperature and Voltage , 1981, IEEE Transactions on Electrical Insulation.

[3]  Gian Montanari.  Electrical life threshold models for solid insulating materials subjected to electrical and multiple stresses. I. Investigation and comparison of life models , 1992, IEEE Transactions on Electrical Insulation.

[4]  Hideo Hirose,et al.  A Method to Estimate the Lifetime of Solid Electrical Insulation , 1987, IEEE Transactions on Electrical Insulation.

[5]  H. Kramers.  Brownian motion in a field of force and the diffusion model of chemical reactions , 1940 .

[6]  Y. Inoue,et al.  Measurement of space charge distribution in XLPE cable insulation at high temperature , 1998, Conference Record of the 1998 IEEE International Symposium on Electrical Insulation (Cat. No.98CH36239).

[7]  Leo Reich,et al.  Elements of polymer degradation , 1971 .

[8]  T. Takada,et al.  An Electric Stress-Pulse Technique for The Measurement of Charges in A Plastic Plate Irradiated by an Electron Beam , 1987, IEEE Transactions on Electrical Insulation.

[9]  G. Mazzanti,et al.  A new thermo-electrical life model based on space-charge trapping , 1996, Conference Record of the 1996 IEEE International Symposium on Electrical Insulation.

[10]  Gian Carlo Montanari,et al.  Aging phenomenology and modeling , 1993 .

[11]  John C. Fothergill,et al.  Electrical degradation and breakdown in polymers , 1992 .

[12]  P. Fischer,et al.  Transient currents in oxidized low-density polyethylene , 1977 .

[13]  Gérard Dreyfus,et al.  New Principle for the Determination of Potential Distributions in Dielectrics , 1977 .

[14]  R. Bartnikas,et al.  Multiple stress aging of solid-dielectric extruded dry-cured insulation systems for power transmission cables , 1994 .

[15]  G. Blaise.  New approach to flashover in dielectrics based on a polarization energy relaxation mechanism , 1993 .

[16]  G. Lessard,et al.  A model of aging of dielectric extruded cables , 1989, Proceedings of the 3rd International Conference on Conduction and Breakdown in Solid Dielectrics.

[17]  Gian Carlo Montanari,et al.  Electrical life threshold models for solid insulating materials subjected to electrical and multiple stresses. II. Probabilistic approach to generalized life models , 1992 .

[18]  L. Dissado,et al.  Electric field enhancement within moulded samples of low density polyethene-a means of failure characterised by voltage ramp tests and space charge measurement , 1996 .

[19]  G. Montanari,et al.  High-field conductivity measurements and search for threshold in PET films , 1996, Proceedings of Conference on Electrical Insulation and Dielectric Phenomena - CEIDP '96.

[20]  T. Ditchi,et al.  Direct measurement of injected charges in insulators submitted to strongly diverging fields using the pressure wave propagation method , 1996, 9th International Symposium on Electrets (ISE 9) Proceedings.

[21]  E. Montroll,et al.  Anomalous transit-time dispersion in amorphous solids , 1975 .

[22]  A. Many,et al.  Theory of Transient Space-Charge-Limited Currents in Solids in the Presence of Trapping , 1962 .

[23]  G. C. Montanari,et al.  The incorporation of space charge degradation in the life model for electrical insulating materials , 1995, IEEE Transactions on Dielectrics and Electrical Insulation.

[24]  William H. Press,et al.  Numerical recipes , 1990 .

[25]  Gerhard M. Sessler,et al.  High-Resolution Laser-Pulse Method for Measuring Charge Distributions in Dielectrics , 1982 .

[26]  Thomas W. Dakin,et al.  Electrical Insulation Deterioration Treated as a Chemical Rate Phenomenon , 1948, Transactions of the American Institute of Electrical Engineers.

[27]  T. W. Dakin,et al.  The voltage endurance of cast and molded resins , 1977, 1977 EIC 13th Electrical/Electronics Insulation Conference.