Space Charge Accumulation at Material Interfaces in HVDC Cable Insulation Part I—Experimental Study and Charge Injection Hypothesis

Abstract

On-site installation of accessories on extruded polymeric high voltage cables in a common practice. The procedure requires the shaping of the physical interface between the cable insulation surface and the pre-molded accessory body. On such interfaces, rough surfaces should be avoided in order to limit space charge accumulation in the insulation, which affects the cable performance by reducing insulation life-time, creating conditions for local field enhancement, and, respectively, the formation of possible breakdown path e.g. by electrical treeing. Space charge measurements on cable insulation peelings were undertaken to assess the space charge injection and accumulation on interfaces with varying degrees of surface roughness in order to improve understanding on this subject. The results of the measurements confirm the hypothesis regarding the enhancement of charge injection from rough surfaces when electric field strength exceeds a certain level. The accumulated charge density in the material is shown to strongly depend on the field strength and temperature in both polarization and subsequent depolarization measurements. These results emphasize that a bipolar charge transport model that incorporates field and temperature dependencies of charge injection, trapping, detrapping, and recombination processes needs to be adopted to accurately describe the observed electric conduction phenomena.

Analysis of Current–Voltage Characteristics in Insulating Polymers Using a Bipolar Charge Transport Model

“…A bipolar charge transport model, already reported in the literature [5,[7][8][9], has been used for the simulations in a low density polyethylene (LDPE). This charge transport model, also called mesoscopic model in the literature for insulating polymers [10], is a hydrodynamic model, based on the advection equation. The model is one dimensional, function of the depth in the sample, and features generation of electronic charges (i.e.…”

Modelling the impact of electrode roughness on net charge density in polyethylene

“…Simulations have been performed with the 2D model, in order to observe the impact of surface roughness on the macroscopic space charge behaviour. Previous studies on the impact of surface roughness on electric field distribution [6,7] have shown that concave defects forming protrusions on the electrode enhance the electric field to a large extent. The field enhancement factor (FEF), i.e.…”

Impact of nanometric processes linked to charge generation on the macroscopic behaviour in polyethylene

“…Charges, generated at the electrodes or inside the bulk, disturb the electric field distribution, leading to local field enhancements, and potentially to an early breakdown. Bipolar charge transport models, also called BCT or mesoscopic models [1][2][3], have been developed this last two decades to predict the electric field distribution within such insulating materials. Electronic charges generation (electrons or holes) at the electrodes are generally described as charge injection, either using the thermionic -i.e.…”

“…Impact of nanometric processes linked to charge generation on the macroscopic behaviour in polyethylene Q.M. Hoang 1 and S. Le Roy 2 1 Faculty of Electrical Engineering, Hanoi University of Industry, Hanoi, Vietnam, 2 LAPLACE, Université de Toulouse, CNRS, INPT, UPS, Toulouse, France…”