Assessment of interfacial charge accumulation in oil-paper interface in transformer insulation from polarization-depolarization current measurements

Polarisasi dan depolarisasi Arus (PDA) analisis biasanya digunakan untuk menentukan kadar air dalam di antara penebat minyak–kertas dan juga konduktiviti minyak di dalam pemboleh ubah. Pengukuran PDA ke atas pemboleh ubah di tapak dilakukan dengan menyuntikkan Voltan DC pada satu sisi pemboleh ubah dan pengukuran arus akak dilalukan pada sisi yang lain, di mana semasa pemdukuran dijalankan pemboleh ubah ini harus dipisahkan dari operasi. Ujian PDC biasanya berjalan sehingga 10000s untuk polarisasi dan harus menunggu 10000s lagi untuk pengukuran depolarisasi. Kerana tempoh ujian yang lama, aplikasi kaedah ini untuk memantau pemboleh ubah yang sedang beroperasi menjadi kurang popular. Dalam kajian ini, sel direka dan dibangunkan untuk melakukan ujian PDA pada sampel minyak penebat. Pola PDA minyak penebat diperoleh dengan ujian menggunakan sel tersebut didapati memiliki pola yang sama dengan ujian dilakukan di tapak. Ramalan kondisi pemboleh ubah dalam perkhidmatan dapat dilakukan dengan melakukan ujian PDA pada sampel minyak penebat yang diambil dari tangki pemboleh ubah dan kemudian membandingkan polanya, tahap konduktiviti dan nilai pemuat berkadar terhadap pola asal PDA minyak penebat tersebut. Kata kunci: Polarisasi; depolarisasi; minyak penebat; pemboleh ubah dan sel Polarization and Depolarization Current (PDC) analysis is normally used to determine the water content in the oil–paper insulation barrier and also oil conductivity inside the transformers. PDC measurement onsite was performed by injecting the DC Voltage at one side of the transformer and current measurement will be carried at the other side of the transformer, in which the transformers are required to be isolated from services to be tested. PDC test normally run up to 10000s for polarization and had to wait for other 10000s for depolarization measurement. Because of the long duration of the test, applications of this method to monitor transformer on service become less popular. In this research, a cell was designed and developed to perform PDC on insulation oil samples. The PDC pattern of insulation oil obtained by testing using the cell was found to have same pattern with the test done onsite. Predictions for transformers in service can be made by performing PDC tests on oil samples taken from the transformer tank and then comparing its pattern, conductivity level and measured capacitance value against a PDC fingerprint. Key words: Polarization; depolarization; oil insulation; transformer; cell

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Space Charge Characteristics of Polypropylene Modified by Rare Earth Nucleating Agent for β Crystallization

Materials ◽

10.3390/ma12010042 ◽

2018 ◽

Vol 12 (1) ◽

pp. 42 ◽

Cited By ~ 2

Author(s):

Jiaming Yang ◽

Mingze Gao ◽

Hong Zhao ◽

Shilin Liu ◽

Ming Hu ◽

...

Keyword(s):

Rare Earth ◽

Space Charge ◽

Impact Resistance ◽

Nucleating Agent ◽

Mechanical Analysis ◽

Mechanical Relaxation ◽

Charge Accumulation ◽

Depolarization Current ◽

High Voltage Direct Current ◽

Lamellar Crystals

Compared to cross-linked polyethylene, polypropylene has a thermoplastic property and the advantage of recycling. However, the poor impact resistance at low temperature and the corresponding space charge problem restrict the application of polypropylene with the extruded high voltage direct current (HVDC) cable. Sufficient introduction of the β form of the polypropylene crystal can significantly improve impact resistance at low temperatures. Although it has been widely applied in insulation engineering, the effect of β-crystal on the space charge characteristics of polypropylene has rarely been researched until now. In this paper, a rare earth nucleating agent of β-crystal is employed to modify the performance of polypropylene to investigate the effects of nucleating agent content on β-crystalline, mechanical relaxation, trap, and space charge characteristics of polypropylene. The results of differential scanning calorimeter (DSC) and X-ray diffraction (XRD) tests indicate that the relative content of β-crystal in modified polypropylene increases gradually with the increasing concentration of the nucleating agent, approaching 43.5% when the nucleating agent content has been raised to 0.2 wt %, suggesting appreciable efficiency of the nucleating agent utilized in our research. Scanning electron microscopy (SEM) is utilized to characterize the morphology of β-crystal spherulites, which illustrates that the β-spherulites are in bunchy shape, and the lamellar crystals are parallel to each other without an obvious boundary between them. The results of the space charge test demonstrate that the modified polypropylene can substantially suppress space charge accumulation, which is attributed to an increment of β-crystal content by adopting a rare earth nucleating agent. It is indicated from dynamic mechanical analysis (DMA) measurements that the enhancement of β-crystalline in modified polypropylene can distinctly increase and decrease the β and α relaxation losses, respectively, which proves that the defects in β-crystal and amorphous regions are reduced and increased respectively. Thermally stimulated depolarization current tests further confirm that the number of traps caused by defects in the β-form of polypropylene crystal declines definitely, which dominantly accounts for the suppression of space charge accumulation.

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Influence of Temperature on Charge Accumulation in Low-Density Polyethylene Based on Depolarization Current and Space Charge Decay

Polymers ◽

10.3390/polym11040587 ◽

2019 ◽

Vol 11 (4) ◽

pp. 587 ◽

Cited By ~ 5

Author(s):

Guochang Li ◽

Jiaxing Wang ◽

Wang Han ◽

Yanhui Wei ◽

Shengtao Li

Keyword(s):

Space Charge ◽

Charge Trapping ◽

Low Density Polyethylene ◽

Low Density ◽

Insulation Material ◽

Charge Accumulation ◽

Depolarization Current ◽

Close Link ◽

Influence Of Temperature ◽

Influence Of Temperature On

Temperature is one of the key factors affecting space charge accumulation in high voltage direct current (HVDC) cable insulation material. The influence of temperature on charge accumulation in low density polyethylene (LDPE) has been investigated with a combined thermally stimulated depolarization current (TSDC) method and pulsed electro-acoustic (PEA) method. The experimental results indicate that there exists a transition temperature region of charge accumulation around 50 °C. The total accumulated charges all firstly increase and then decrease with the increasing polarization temperature under three typical polarization electric fields, and they have more accumulated charges in LDPE around 50 °C. The phenomenon has a close link with the dynamic processes of charge trapping and de-trapping, which were verified by TSDC results. At room temperature, the trapped charges are difficult to release from the traps, and these homocharges near the cathode can depress the further injection of the charges. More charges can be injected from the electrodes with the increase of temperature, while the charge migration is relatively lower before 50 °C, leading to more accumulated charges. When the temperature exceeds around 50 °C, the molecular movement is accelerated which can enhance the hopping probability of charges between the adjacent traps, resulting in few accumulated charges.

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Enhancing dielectric strength of thermally conductive epoxy composites by preventing interfacial charge accumulation using micron-sized diamond

Composites Science and Technology ◽

10.1016/j.compscitech.2021.109178 ◽

2021 ◽

pp. 109178

Author(s):

Kerong Yang ◽

Weijiang Chen ◽

Yushun Zhao ◽

Lijian Ding ◽

Bin Du ◽

...

Keyword(s):

Dielectric Strength ◽

Epoxy Composites ◽

Charge Accumulation ◽

Thermally Conductive ◽

Interfacial Charge

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Influence of temperature on interfacial charge of power transformer insulation

IET Science Measurement & Technology ◽

10.1049/iet-smt.2018.5668 ◽

2019 ◽

Vol 13 (7) ◽

pp. 1059-1067 ◽

Cited By ~ 2

Author(s):

Saurabh Dutta ◽

Deepak Mishra ◽

Nasirul Haque ◽

Arpan Kumar Pradhan ◽

Arijit Baral ◽

...

Keyword(s):

Power Transformer ◽

Influence Of Temperature ◽

Influence Of Temperature On ◽

Transformer Insulation ◽

Interfacial Charge

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Improved DC Dielectric Performance of Photon-Initiated Crosslinking Polyethylene with TMPTMA Auxiliary Agent

Materials ◽

10.3390/ma12213540 ◽

2019 ◽

Vol 12 (21) ◽

pp. 3540 ◽

Cited By ~ 3

Author(s):

Peng Qiu ◽

Jun-Qi Chen ◽

Wei-Feng Sun ◽

Hong Zhao

Keyword(s):

Space Charge ◽

First Principles ◽

First Principles Calculations ◽

Charge Accumulation ◽

Depolarization Current ◽

Trapping Mechanism ◽

Crosslinking Process ◽

Deep Traps ◽

Molecular Group ◽

Dielectric Performance

To achieve high direct current (DC) dielectric performance of crosslinked polyethylene (XLPE) applied for insulated cable, the auxiliary crosslinking agent of trimethylolpropane trimethacrylate (TMPTMA) is employed in photon-initiated crosslinking process to the present polar-molecular group which will introduce deep traps for charge carriers. The space-charge accumulation and electrical conductance of XLPE are observably suppressed due to the deep traps deriving from the TMPTMA crosslinkers that are chemically connecting (grafted onto) polyethylene molecules. Thermally stimulated depolarization current tests and first-principles calculations consistently demonstrate a trapping mechanism of impeding charge injection and carrier transport in XLPE with TMPTMA crosslinkers. The characteristic cyclic anhydrides with coupled carbonyl groups are used as auxiliary crosslinkers to promote crosslinking efficiency and provide polar groups to polyethylene molecules which can be effectively fulfilled in industrial cable production. The results of infrared spectroscopy show that the auxiliary crosslinkers have been successfully grated to polyethylene molecules through the UV-initiation process. The space-charge characteristics achieve a significant improvement consistent with the theoretical estimation that deeper electronic traps can be introduced by auxiliary crosslinker and will consequently suppress space-charge accumulation through a trapping mechanism. Meanwhile, the conductivity of XLPE observably increases after using TMPTMA auxiliary crosslinkers at various temperatures of cable operation. The first-principles calculations also demonstrate that substantial electronic bound states have been introduced at the band edge of polyethylene molecules crosslinked by TMPTMA, leading to reduction in electrical conductivity. On the advantage of ameliorating DC dielectric performance by way of UV-initiated crosslinking process, the present research suggests a substantial strategy in XLPE cable industrial productions.

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