Comparing simulation results and experimental measurements of electroluminescence phenomenon in dielectric materials

Abstract

Under continuous application of high electrical stresses, the insulation system of an underground power cable is subjected to long-term degradation that can eventually cause premature breakdown of the cable. This is as a result of electronic charges being injected into the dielectric material when intense electric field is applied. These charges will then interact with polymer molecules; causing even more charges to accumulate within the vicinity of the material and thus further deterioration. The interaction of the charges can lead to the dissipation of energy in the form of photons; a process known as electroluminescence (EL). In addition to space charge probing, the measurement of EL has becoming increasingly prominent in understanding the mechanisms that contribute to the early electrical ageing of an insulating material. This paper attempts to simulate EL behaviour based on the underlying hypotheses of charge injection and bipolar recombination processes that take place within a polymer. A detailed comparison between the computation results and the experimental measurements carried out by different researchers will be discussed in order to evaluate the mechanisms responsible for this phenomenon.

Modeling electroluminescence in insulating polymers under ac stress: effect of excitation waveform

“…The model is able to reproduce the experimental data, especially in terms of the phase angle between EL and the applied voltage as well as the shape of the EL distribution within each half cycle of the applied voltage. More recently, Ariffin et al [11] have developed a model based on the same concepts but considering a smaller penetration depth (order of 10 nm) of the injected charges into the dielectric. Phase angle between EL and applied stress is correctly described.…”

“…Supposing that EL emission pattern reflects the field at the injecting electrode, for explaining the phase advance of EL in respect to applied field (typically 30-40°for uniform field configuration), the amount of stored charge must be such that the space charge-induced field represents 20% of the applied crest field. In previous models, the order of magnitude of the space charge density allowing field mediation at the injecting electrode in a uniform field configuration is typically 0.1 C.m -3 when considering a 100 µm space charge layer [9]; it is of 10 +4 C.m -3 when considering a carrier penetration depth of 10 nm as in [11] with quite different applied field amplitude. Having said so, the question that is raised is the physical soundness of these models.…”

Contribution to the modelling of electroluminescence in high voltage polymeric materials

“…Only a brief description is given here, more details of this model are given in [1]. Transport, diffusion and extraction of charge at the electrodes are not accounted for.…”

“…Recently, an electroluminescence model has been developed at Southampton [1] by examining the changes to the electric field at the injecting electrode due to the presence of the injected charge carriers. This model is based on current injection and recombination processes in a dielectric material.…”