Space Charge Measurement and Modelling in Cross-Linked Polyethylene

Abstract

Cross-linked polyethylene, commercially known as XLPE, is widely used as an insulating material in high voltage cables. However, space charge accumulation under the DC field is one of the most challenging problems in the further development of XLPE insulated cable. Due to the potential electrical degradation ageing process triggered by the accumulated space charges, the IEEE standard 1732 was established for measuring space charge in HVDC extruded cables as the qualification tests. Previous research has revealed that space charge originates from either charge injection at the electrodes or ionization of impurities presenting inside the bulk. In the light of this, this paper aims to simulate the accumulation of space charge in XLPE under DC stress. Space charge measurements have been carried on the fresh and degassed XLPE samples. A modified bipolar charge transport model, by considering the dissociation of impurities, has been employed to simulate the space charge behavior in XLPE. Compared with the experimental observations, the simulation results can reveal appropriate features of hetero charge formation. Both the calculated charge dynamics and field variation are consistent with the experiment results. The restrictions and potential improvements of this preliminary model are also discussed for its future application of XLPE cables.

Impact of accelerated aging of epoxy‐Ni nanocomposites on space charge variation adopting pulsed electro acoustic technique

“…Hetero‐charge formation occurs due to the ionization of impurities such as dangling chain ends that are formed due to the thermally induced degradation reactions. [ 29 ] Due to thermal exposure, the molecular structure undergoes structural deterioration in the form of chain scissions and oxidation reactions resulting in more number of trapping sites. [ 19 ] This led to the formation of hetero‐charges.…”

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

“…Regarding PEA data processing, to avoid interference of capacitive charges that are overlapped with the space charges and reveal true charge distribution, the reference data obtained at low electric field was used to subtract the surface charges near the electrodes at high field and the normalised voltage‐on space charge density $${\rho }_{\text{nor}}(\mathit{x},\mathit{t})$$ was obtained with equation () below, $$${\rho }_{\text{nor}}(\mathit{x},\mathit{t})={\rho }_{\text{exp}}(\mathit{x},\mathit{t})-\frac{{\mathit{E}}_{\text{appl}}}{{\mathit{E}}_{\text{ref}}}\cdot {\rho }_{\text{ref}}(\mathit{x})$$$ where x is the distance to the cathode; t is the field application time; $${\rho }_{\text{ref}}(\mathit{x})$$ and $${\rho }_{\text{exp}}(\mathit{x},\mathit{t})$$ represents the charge density of the reference data and experimentally measured data at point x and time t , respectively; $$\,{\mathit{E}}_{\text{ref}}$$ and $${\mathit{E}}_{\text{appl}}$$ are the reference and applied electric field, respectively [32, 33]. Local electric field distortion rate was calculated using equation (), $$$\text{Field}\,\text{distortion}\,\text{rate}=\,\frac{{\mathit{E}}_{\text{act}}-{\mathit{E}}_{\text{appl}}}{{\mathit{E}}_{\text{appl}}}\,\times 100\,\%$...$$…”

“…where x is the distance to the cathode; t is the field application time; ρ ref ðxÞ and ρ exp ðx; tÞ represents the charge density of the reference data and experimentally measured data at point x and time t, respectively; E ref and E appl are the reference and applied electric field, respectively [32,33]. Local electric field distortion rate was calculated using equation ( 3),…”

Effect of multi‐factors on heterocharges for oil‐impregnated paper in converter transformer using modified charge transport model

“…Impurities (AB) in oil‐impregnated paper are dissociated under the electric field, then positive ions (A + ) and negative ions (B ‐ ) are produced [16]. The charge transport model is shown in Figure 1.…”