A study on the space charge formation in XLPE

IEEE Trans. Dielect. Electr. Insul.

et al. 2014

The occurrence of ageing of cross-linked polyethylene (XLPE) cable insulation greatly affects the safe operation of cable system. The influence of different ageing modes on the space charge dynamics and physicochemical properties of insulating materials in highvoltage alternating current (HVAC) XLPE cables was investigated. The XLPE specimens were obtained from un-aged cables, 1-year laboratory accelerated aged cables, and 22-year practical cables. Pulsed Electro-Acoustic (PEA) technique was used to measure the space charge dynamics and accumulation properties in the aged XLPE insulation. Differential Scanning Calorimetry (DSC) and Fourier-Transform Infrared (FTIR) were used to reveal the details of their physicochemical properties. It was found that the homocharge accumulated at the aluminum (Al) electrode for the un-aged cables, while the hetero-charge for aged cable insulations. The total amount of homo-charge near anode decreases with temperature for un-aged specimens, while the amount of hetero-charge increases with temperature for aged specimens. It was suggested that, the homo-charge results from charge injection of electrodes, and the hetero-charge appear to be intimately related with the ionization of ageing products in XLPE insulation. Additionally, the total charge of un-aged cables and 22-year practical cables increased along the radial direction from inner to outer, whereas the total charge of 1-year accelerated aged cables decreased. It was suggested that accelerated ageing of cables starts from the inside of the insulating materials, while ageing of 22-year practical cables starts from the outside. It was also found that two new absorption peaks appeared in FTIR spectrums of aged specimens around 1720 cm -1 and 3500 cm -1 , and the carbonyl groups increase with ageing time. The crystallization morphology, impurity particles ionization, injection and transportation of charges show great effect on the space charge dynamics.

Section: Cable Insulation Ageingmentioning

confidence: 99%

Physicochemical origin of space charge dynamics for aged XLPE cable insulation

IEEE Trans. Dielect. Electr. Insul.

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

“…Much research has shown that a few factors can be associated with the formation of space charge in XLPE, such as the crosslinking structure, anti-oxidants and moisture [4]. However, it is believed that crosslinking byproducts are one of the major contributors in space charge accumulation [5] which is why a degassing process is applied to remove byproducts from the crosslinked structure after the crosslinking process. This paper intends to gain a deeper understanding of space charge accumulation mechanisms in XLPE and address how individual byproducts can affect space charge formation within the polymer.…”

Section: Introductionmentioning

confidence: 99%

Analysis of space charge formation in LDPE in the presence of crosslinking byproducts

Hussin

Chen

2012

Cross-linking byproducts are suspected to be the main contributing factor in space charge formation observed in XLPE. To investigate the mechanism behind this phenomenon, low density polyethylene was soaked into three main crosslinking byproducts, acetophenone, -methylstyrene and cumyl alcohol, and space charge measurements were performed using the Pulse Electroacoustic technique (PEA). It has been found that soaking LDPE in cumyl alcohol introduces more charges into the system, with homocharges and heterocharges accumulating within the sample compared to the additive free sample. In contrast, -methylstyrene and acetophenone reduce the amount of accumulated charges. In terms of charge decay, all three byproducts enhance the decay process in the insulator. Further investigations were conducted in conditions where two byproducts are present in a sample. The results shows that acetophenone is a dominant byproduct in determining the charge density patter built up during the charging process, whilst the rate of charge decay is observed to be high in the presence of -methylstyrene in the sample.

“…Furthermore, the larger the trap density was, the lower the interface electric field was. For further explanation for TiO 2 -XLPE interface, taking cathode electron injection as an example, an electron accumulation area is formed near the interface, and its width is shown in formula (2) [26]. It can be seen that the larger the trap density , the narrower the width of the electron accumulation area and the larger the reverse electric field.…”

Section: Discussionmentioning

confidence: 99%

Effect of Nanoparticle Surface Modification and Filling Concentration on Space Charge Characteristics in TiO₂/XLPE Nanocomposites

Xiao

Journal of Nanomaterials

et al. 2016

This paper focuses on the space charge characteristics in TiO 2 /cross-linked polyethylene (XLPE) nanocomposites; the unmodified and modified by dimethyloctylsilane (MDOS) TiO 2 nanoparticles were added to XLPE matrix with different mass concentrations (1 wt%, 3 wt%, and 5 wt%). The scanning electron microscope (SEM) showed that the MDOS coupling agent could improve the compatibility between TiO 2 nanoparticles and XLPE matrix to some extent and reduce the agglomeration of TiO 2 nanoparticles compared with unmodified TiO 2 nanoparticles; the volume resistivity testing indicated that the volume resistivity of TiO 2 /XLPE nanocomposites was higher than Pure-XLPE and increased with the increase of filling concentrations. According to the pulsed electroacoustic (PEA) measurements, it was concluded that the space charge accumulation was suppressed by filling TiO 2 nanoparticles and the distribution of electric field in samples was improved greatly. In addition, it was found that the injection of homocharge was more obvious in MDOS-TiO 2 /XLPE than that in UN-TiO 2 /XLPE and the homocharge injection decreased with the increase of filling concentration.