6,090 research outputs found
Calibration of the Pulsed Electroacoustic Technique in the Presence of Trapped Charge
No full textThe influence of pulse voltage on the accuracy of charge density distribution in the pulsed electroacoustic technique (PEA) is discussed. It is shown that significant error can be introduced if a low dc voltage and high pulse voltage are used to calibrate charge density. However, our main focus in the present paper is to deal with one of the practical situations where space charge exists in the material prior to any measurements. The conventional calibration method can no longer be used to calibrate charge density due to the interference by the charge on the electrode induced by space charge. A method has been proposed which is based on two measurements. Firstly, the sample containing charge is measured without any applied voltage. The second measurement is carried out with a small external applied voltage. The applied voltage should be small enough so there is no disturbance of the existing charge in the sample. The difference of the two measurements can be used for calibration. An additional advantage of the proposed method avoids the influence of the pulse voltage on calibration and therefore gives a more accurate representation of space charge. The proposed method has been validated
Replication Data for: Topologically Enhanced Harmonic Generation in a Nonlinear Transmission Line Metamaterial
No full textData and computer code used to produce the experiment and theory plots in the paper "Topologically Enhanced Harmonic Generation in a Nonlinear Transmission Line Metamaterial" by Y. Wang, L.-J. Lang, C. H. Lee, B. Zhang, and Y. D. Chong
The effect of degassing on morphology and space charge
No full textIt is believed that space charge buildup in cross-linked polyethylene (XLPE) insulation is the main cause for premature failure of underground power cables. The space charge activities in XLPE depend on many factors such as additives, material treatment, ambient temperature, insulator/electrode interface, etc. Degassing is one of the material treatment process commonly employ in cable manufacturing to improve insulation performance. In this paper, investigation on the effect of degassing period has on the morphology and space charge was carried out. Planar XLPE samples of the same composite were subjected to different degassing time. It is discovered that apart from removing volatile by-products, degassing also anneal XLPE material; changing the morphology as a result
Temperature effect on space charge dynamics in XLPE insulation
No full textThis paper reports on space charge evolution in crosslinked polyethylene (XLPE) planar samples approximately 1.20 mm thick subjected to electric stress level of 30 kVdc/mm under four temperature 25 oC, 50 oC, 70 oC and 90 oC for 24 hours. Space charge profiles in both as-received and degassed samples were measured using the laser induced pressure pulse (LIPP) technique. The dc threshold stresses at which space charge initiates are greatly affected by testing temperatures. The results suggest that testing temperature has numerous effects on space charge dynamics such as enhancement of ionic dissociation of polar crosslinked by-products, charge injection, charge mobility and electrical conductivity. Space charge distributions of very different nature were seen at lower temperatures when comparing the results of as-received samples with degassed samples. However at higher temperature, the space charge distribution took the same form, although of lower concentration in degassed samples. Space charge distributions are dominated by positive charge when tested at high temperatures regardless of sample treatment and positive charge propagation enhances as testing temperature increases. This can be a major cause of concern as positive charge propagation has been reported to be related to insulation breakdown
Space charge and charge trapping characteristics of cross-linked polyethylene subjected to ac electric stresses
No full textThis paper reports on the result of space charge evolution in cross-linked polyethylene (XLPE) planar samples of approximately 220 ?m thick. The space charge measurement technique used in this study is the PEA method. There are two phases to this experiment. In the first phase, the samples were subjected to dc 30 kVdc/mm and ac (sinusoidal) electric stress level of 30 kVpk/mm at frequencies of 1 Hz, 10 Hz and 50 Hz ac. In addition, ac space charge under 30 kVrms/mm and 60 kVpk/mm electric stress at 50 Hz was also investigated. The volts off results showed that the amount of charge trapped in XLPE sample under dc electric stress is significantly bigger than samples under ac stress even when the applied ac stresses are substantially higher. The second phase of the experiment involves studying the dc space charge evolution in samples that were tested under ac stress during the first phase of the experiment. Ac ageing causes positive charge to become more dominant over negative charge. It was also discovered that ac ageing creates deeper traps, particularly for negative charge. This paper also gave a brief overview of the data processing methods used to analyse space charge under ac electric stress
A Novel Calibration Method in the Presence of Space Charge in Dielectric Materials Using the Pulsed Electroacoustic Technique
No full textCalibration is an important part of procedures to accurate measurements of space charge in solid dielectrics. The pulsed electroacoustic (PEA) technique is one of the mostly used techniques due to its simplicity in construction, low cost and easy to implement for both plaque and cable samples. A novel method has been proposed which enables the PEA technique to be used in the presence of space charge. It is based on two measurements. Firstly, the sample with the presence of charge is measured without any applied voltage. The second measurement is carried out with a small dc applied voltage. The applied voltage should be small enough so there is no disturbance on the existing charge in the sample. The difference of the two measurements can be used for calibration. The additional advantage of the proposed method avoids the influence of the pulse voltage on calibration. A 200 µm LDPE sample was stressed at 8 kV for 60 minutes to produce a significant amount of charge in the sample. The proposed method has been used to calculate the residual charge and the result has been compared with the conventional method
Effect of the length of degassing period on the space charge dynamic in XLPE insulation under DC stressing condition
No full textIn this paper, the space charge measurement results obtained from planar samples of XLPE (made by Borealis XL4201S) over a 24 hours Dc ageing are reported. Some preliminary results on the effect of the sample degassing period on space charge distribution in the XLPE material are discussed, and comparative study between as-received and degassed XLPE samples with different length of degassing period (degassed for 6, 12, 24 and 48 hours at 60OC) are also be presented
Optimization of the aluminium target thickness on the space charge measurement using LIPP technique
No full textIn this paper, the influence of the aluminium disc thickness on the acoustic reflection, spatial resolution of 1.2mm and 2mm XLPE plaque in space charge measurement using LIPP system will be studied. Preliminary results obtained from 2mm as-received and degassed planar XLPE samples subjected to dc electric stresses of 30kV/mm (at room temperature) for 24 hours using the optimum aluminium thickness are reported. Comparative study between as-received and degassed XLPE samples is also presented
Temperature effect on the space charge characteristics in as-received and degassed XLPE insulation under DC stressing condition
No full textThis paper reports on an investigation into the effect of temperature on space charge dynamics in ~2 mm thick as-received and degassed XLPE plaques. The samples were stressed at 30 kV/mm under dc condition for 24 hours. Measurements of space charge profiles were made at various times using our newly automated laser induced pressure pulse (LIPP) system. Emphasis has been placed on the comparison of space charge characteristics between as-received and degassed XLPE plaques at four different temperatures (i.e. 25OC, 50OC, 70OC and 90OC). Significant difference in space charge dynamics has been observed between as-received and degassed samples. It has been found that temperature has an important effect on both the rate of space charge build up and the amount of charge formed in the bulk
Effect of Morphology on Space Charge Dynamics In Polyethylene Insulation (invited plenary lecture)
No full textPolymeric insulation has been progressively replaced traditional paper impregnated insulation. Electrical performance of polymeric materials is determined by many factors. One of them is morphological feature of polymer. Effects of morphological change on electrical performance of polyethylene insulation have been studied due to its technological importance in high voltage power cable system. The results obtained so far, however, are inconclusive. One of the reasons is the complicated relationship between electrical performance and morphology. It has been suggested that the presence of space charge may play a significant role in determining electrical performance of polyethylene insulation. In this paper space charge formation in low density (LDPE) with different morphological features at various temperatures were investigated. Different morphologies were realized via addition of antioxidant which serves as nucleation centres. The space charge dynamics were observed at room temperature, 50, and 70 °C under high voltage application using the pulsed electro-acoustic (PEA) method. It has been found that the morphology change in LDPE does not result in significant changes in charge accumulation. On the other hand the introduction of antioxidants into LDPE leads to negative charge accumulation at high temperatures, indicating the creation of deep traps. In addition space charge in XLPE samples was also measured using the laser induced pressure pulse technique (LIPP). It has been found that heterocharge accumulation in XLPE is greatly affected by heat treatment. The results are discussed in terms of reduction in crosslinking by-products concentration and morphological change caused by the heat treatment. It seems that the space charge in XLPE is more to do with the by-products rather than morphological change
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