The Impact of Cross-Linking Effect on the Space Charge Characteristics of Cross-Linked Polyethylene with Different Degrees of Cross-Linking under Strong Direct Current Electric Field

Abstract

Cross-linked polyethylene (XLPE) obtained by the crossing-linking reaction of polyethylene (PE) can greatly enhance the mechanical properties and other properties of PE, which makes XLPE widely applied in the field of electric power engineering. However, the space charges can distort the distribution of the electrical field strength in the XLPE applied in the insulation materials, which can shorten the service life of the insulation materials. Therefore, the space charge characteristics of XLPE under the strong direct current (DC) electric field have been the focus of scholars and engineers all over the world. This article has studied the impact of the cross-linking effect on the space charge characteristics of XLPE with different degrees of cross-linking. For this issue, we used dicumyl peroxide (DCP) as the cross-linking agent and low-density polyethylene (LDPE) as the base material for the preparation of samples. Besides, the space charge distribution was measured by the pulsed electro-acoustic method (PEA). In addition, the average charge density as a characteristic parameter was introduced into the experiment, which was used to quantitatively analyze the impact of the cross-linking effect on the space charge characteristics of XLPE with different degrees of cross-linking. Meanwhile, we also explained the impact of the cross-linking effect on XLPE with different degrees of cross-linking from a microscopic point of view. Ultimately, some important conclusions can be obtained. For instance, the cross-linking effect significantly increases the threshold electrical field strength of XLPE, and as the content of cross-linking agent increases, the threshold electrical field strength increases at first and then decreases, and the threshold electrical field strength reaches the maximum value when the content of the cross-linking agent is 1.0% or 2.1%. Besides, the cross-linking effect introduces negative charge traps into the LDPE and increases the densities of the deeper charge traps, and so on. In addition, we have also analyzed the average charge density, and we have summarized the theoretical model of the average charge decay, namely, Q ( t ) = Q 0 + α e − t β , which is very effective for explaining the dissipation characteristics (more conclusive contents can be seen in the conclusion section of this article).

Caryophyllene as a Precursor of Cross-Linked Materials

“…Obtaining a higher amount of gel fraction with DCP compared to with BPO was already identified in other studies. 31,32 Indeed, DCP is the most frequently used cross-linking agent since it is an organic peroxide which is more selective to vinyl moieties than benzoyl peroxide. 33,34 The ability of cumyloxy radical from DCP to react with non-activated vinyl moieties in a free-radical cross-linking pathway via H abstraction may be a possible explanation of its higher reactivity compared to BPO.…”

Functionalization of Silica Nanoparticles to Improve Crosslinking Degree, Insulation Performance and Space Charge Characteristics of UV-initiated XLPE

“…In order to further quantitatively analyze space charge accumulations in the prepared nanocomposites with modified dielectric performances at elevated temperatures, the average space charge densities under 40 kV/mm electric field after polarizing for 3600 s are calculated according to the formula defined as follows [ 35 , 36 ]: where q p ( x , t , E P ) denotes the internal space charge density at position x ; t represents polarization time; E P symbolizes the applied electric field magnitude; x 0 and x 1 identify the interior positions at the down and up electrodes, respectively. It is indicated from the calculation results shown in Figure 12 a that the average charge density of all samples except 0.5wt%TAIC- s -SiO 2 /XLPE nanocomposite increases with the increasing temperature, confirming that temperature elevation will exacerbate space charge injections from both electrodes, which is mostly intensified in pure XLPE.…”

Influence of Thermal Aging on Space Charge Accumulation and Dissipation of Cross-Linked Polyethylene With Different Cross-Linking Agent Contents

“…In addition, we have followed the reference [20] to prepare pure LDPE samples and XLPE samples with 1.0%, 2.1%, 3.0%, and 5.0% DCP. And the size of these samples was all 4 cm × 4 cm × approximate 160 μm.…”