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The effects of charge carrier injection and intrinsic ionic carriers on the conduction process in superclean low-density polyethylene and cross-linked polyethylene (LDPE and XLPE) and the associated development of space charge are investigated. The carrier mobility is measured directly by space charge measurements in a double- and triple-layer structure. It is shown that the difference between superclean LDPE and XLPE in the field-dependence of the current density results from the dominance of ions in XLPE introduced by cross-linking as compared to injected carriers in the case of superclean LDPE. [ABSTRACT FROM AUTHOR]

The time function of the Eyring reaction rate theory of insulation life is modified to demonstrate a physical origin for temperature threshold. Various mechanisms by which trapped charges may be involved in degrading the polymer are examined, and incorporated into the life model through an alteration to the free energies of the reacting system. The corresponding life functions are shown to possess the field-dependent threshold form previously obtained phenomenologically for insulating materials. The physical interpretation of the model parameters is discussed.

A model is presented that addresses the energy stability of localized electron states in insulating polymers with respect to delocalized free electron-like states at variable charge densities. The model was derived using an effective Hamiltonian for the total energy of electrons trapped in large polarons and spin-paired bipolarons, which includes the electrostatic interaction between charges that occurs when the charge density exceeds the infinite dilution limit. The phase diagram of the various electronic states with respect to the charge density is derived using parameters determined from experimental data for polyethylene, and it is found that a phase transition from excess charge in the form of stable polarons to a stable state of bipolarons with charge=2 and spin number S=0 is predicted for a charge density between 0.2 C/m3 and ~2 C/m3. This transition is consistent with a change from low mobility charge transport to charge transport in the form of pulses with a mobility orders of magnitude higher that has been observed in several insulating polymers. [ABSTRACT FROM AUTHOR]

A previously unknown mode of conduction is identified in insulating polymers at moderate fields (40-50 MV/m). This takes the form of coherent charged pulses with a mobility (∼10-10 m2V-1s-1) several orders of magnitude larger than that traditionally associated with independent charge carriers (∼10-14 m2V-1s-1). It is shown that this phenomenon is consistent with a mechanism in which a charged compression boundary is formed electro-mechanically during injection and thereafter travels as a coherent solitary wave (soliton) through the polymer. [ABSTRACT FROM AUTHOR]

A simulation model to investigate the statistical property of electrical breakdown is presented based on the field-assisted percolation model for dielectric breakdown, by expressing the disorder in morphology as randomly distributed trap barriers. The effects of sample area and large defects on the statistical property of breakdown are also studied, and the statistical behavior of the lifetime is investigated by considering the stochastic development of deteriorated regions. In addition an equation describing the breakdown probability in homogeneous materials is derived from percolation theory, which we show fits well to the simulation data. The breakdown probability is expressed in terms of trap distribution, and thus provides a way to connect the disorder in polymer morphology with the stochastic nature of breakdown. [ABSTRACT FROM AUTHOR]

We introduce and develop two bipolar transport models which are based on appreciably different physical assumptions regarding the distribution function in the energy levels of trap states. In the first model, conduction is described by an effective mobility of the carriers and the accumulation of stored space charge is taken into account through a single trapping level. In the second model the hypothesis of an exponential distribution function of trap depth is made, with conduction taking place via a hopping process from site to site. The results of simulations of the two models are compared with experimental data for the external current and the space-time evolution of the electrical space charge distribution. The two descriptions are evaluated in a critical way, and the prospects for these models to adequately describe real systems are given. [ABSTRACT FROM AUTHOR]

Deals with a study which used calculable fractal circuit models to show that the cluster model response functions result from the combination of two types of self-similarity. Cluster model response functions; Dielectric response and deterministic fractal circuits; Molecular scale fractal interpretation of the cluster model; Interpretation of dielectric measurements.

The requirement of insertion of optical amplifier units and joints, into long-distance submarine telecommunication systems, results in regions of the polymeric insulation which have to be reinstated, using injection molding techniques. These techniques introduce internal amalgamated interfaces, which subsequently can be the sites of possible electrical insulation failure in the system. Studies [1-3] have proposed that the increased risk of failure is associated with the development of stress enhancing space charge at these interfaces. This paper reports on space charge measurements, (using the pulsed electroacoustic (PEA) technique [4]), from microtomed thin film samples taken from the interface region of typical system joints which have undergone accelerated aging tests under a dc voltage at room temperature. The space charge distributions obtained for the samples are discussed with reference to the underlying mechanisms of both the bulk low-density polyethylene (LDPE) and the surface (LDPE/electrode interface). The effect of varying the electrode material (i.e. Au and Al) is discussed with reference to previously published data. Finally the effects of long-term aging on space charge accumulation within LDPE are considered briefly.