scholarly journals Precise Measurements of the Temperature Influence on the Complex Permittivity of Power Transformers Moistened Paper-Oil Insulation

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5802
Author(s):  
Pawel Zukowski ◽  
Przemyslaw Rogalski ◽  
Konrad Kierczynski ◽  
Tomasz N. Koltunowicz
Keyword(s):  
Relaxation Time ◽  
Complex Permittivity ◽  
High Frequency ◽  
Solid Component ◽  
Power Transformers ◽  
Insulating Oil ◽  
Polarization Mechanism ◽  
Two Stages ◽  
Permittivity Component ◽  
Made In

The reference characteristics of complex permittivity of the transformers insulation solid component were determined for use in the precise diagnostics of the power transformers insulation state. The solid component is a composite of cellulose, insulating oil and water nanoparticles. Measurements were made in the frequency range from 10−4 Hz to 5000 Hz at temperatures from 293.15 to 333.15 K. Uncertainty of temperature measurements was less than ±0.01 K. Pressboard impregnated with insulating oil with a water content of (5.0 ± 0.2) by weight moistened in a manner maximally similar to the moistening process in power transformers was investigated. It was found that there are two stages of changes in permittivity and imaginary permittivity components, occurring for low and high frequency. As the temperature increases, the frequency dependencies of the permittivity and imaginary permittivity component shifts to the higher frequency region. This phenomenon is related to the change of relaxation time with the increase in temperature. The values of relaxation time activation energies of the permittivity ΔWτε′ ≈ (0.827 ± 0.0094) eV and the imaginary permittivity component ΔWτε″ = 0.883 eV were determined. It was found that Cole-Cole charts for the first stage are asymmetric and similar to those described by the Dawidson–Cole relaxation. For stage two, the charts are arc-shaped, corresponding to the Cole-Cole relaxation. It has been established that in the moistened pressboard impregnated with insulating oil, there is an additional polarization mechanism associated with the occurrence of water in the form of nanodrops and the tunneling of electrons between them.

Core loss behavior in high frequency high power transformers—II: Arbitrary excitation

2012 ◽  
Vol 4 (3) ◽  
pp. 033113 ◽  
Author(s):  
E. Agheb ◽  
M. A. Bahmani ◽  
H. K. Høidalen ◽  
T. Thiringer
Keyword(s):  
High Power ◽  
High Frequency ◽  
Core Loss ◽  
Power Transformers

The first two decades of Circular Economy in the 21st century: a bibliographic review

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
João Francisco Pinto Anaruma ◽  
Jorge Henrique Caldeira de Oliveira ◽  
Francisco Anaruma Filho ◽  
Wesley Ricardo de Souza Freitas ◽  
Adriano Alves Teixeira
Keyword(s):  
21St Century ◽  
Circular Economy ◽  
Review Of Literature ◽  
Content Type ◽  
Time Period ◽  
Number Of Publications ◽  
Two Stages ◽  
Academic Area ◽  
Practical Implications ◽  
Made In

PurposeThe purpose of this paper is to analyze and map the main areas of the Circular Economy literature of the first two decades of 21st century, offering a broad vision about the growth of the theme during these years.Design/methodology/approachThe research was divided into two stages: the first was a systematic review of literature and the second consisted on generation and analysis of bibliographic maps.FindingsThe publication indicates the prominence of China and European Union countries in the production of articles about Circular Economy. Furthermore, the topic is restricted to academic area, and that research on Circular Economy is still very focused on theory studies, even with exponential growth in the number of published articles about the theme since 2015. Finally, it also provides a collection of information as the principal authors, the most cited publications, citations, co-citations and countries that have most published beyond which are the most discussed topics.Research limitations/implicationsA possible limitation of the research is that it was performed only in the Scopus database. It may be suggested as future searches that other databases are included as well, and another suggestion is to reduce the time period between research samples due to the exponential increase in the number of publications and topics discussed lately.Practical implicationsThe results of this paper can guide future researches about the development of Circular Economy during the next decades or years and serve as a facilitator for researchers and for managers that want to know more about the topic.Originality/valueA mapping of the principal players and main discussions about Circular Economy made in the first two decades of the 21st century and an analysis about the growth and changes about the theme.

The locust jump. I. The motor programme

1977 ◽  
Vol 66 (1) ◽  
pp. 203-219
Author(s):  
W. J. Heitler ◽  
M. Burrows
Keyword(s):  
High Frequency ◽  
Tactile Stimulation ◽  
The Body ◽  
Flexor Muscle ◽  
Tactile Stimuli ◽  
Extensor Muscles ◽  
Trigger Activity ◽  
Three Stages ◽  
Motor Programme ◽  
Made In

A motor programme is described for defensive kicking in the locust which is also probably the programme for jumping. The method of analysis has been to make intracellular recordings from the somata of identified motornuerones which control the metathoracic tibiae while defensive kicks are made in response to tactile stimuli. Three stages are recognized in the programme. (1) Initial flexion of the tibiae results from the low spike threshold of tibial flexor motorneurones to tactile stimulation of the body. (2) Co-contraction of flexor and extensor muscles followa in which flexor and extensor excitor motoneurones spike at high frequency for 300-600 ms. the tibia flexed while the extensor muscle develops tension isometrically to the level required for a kick or jump. (3) Trigger activity terminates the co-contraction by inhibiting the flexor excitor motorneurones and simultaneously exciting the flexor inhibitors. This causes relaxation of the flexor muscle and allows the tibiae to extend. If the trigger activity does not occur, the jump or kick is aborted, and the tibiae remain flexed.

Hypersonic Velocity, Absorption and Relaxation in Molten CSNO3

1977 ◽  
Vol 32 (1) ◽  
pp. 57-60 ◽  
Author(s):  
H. E. Gunilla Knape ◽  
Lena M. Torell
Keyword(s):  
Relaxation Time ◽  
High Frequency ◽  
Viscosity Coefficient ◽  
Sound Waves ◽  
Frequency Range ◽  
Ultrasonic Velocities ◽  
Hypersonic Velocity ◽  
Frequency Shifts ◽  
Bulk Viscosity Coefficient ◽  
Good Agreement

Abstract Brillouin spectra of molten CSNO3 were investigated for scattering angles between 40 and 140° and in a temperature interval of 420-520 °C. An Ar+ singlemode laser was used for excitation and the total instrumental width was ~265 MHz. The measured frequency shifts and linewidths of the Brillouin components were used to determine velocities and attenuations of thermal sound waves in the frequency range 2.3-7.0 GHz. A dispersion of 4-5% was found between the present hyper­ sonic velocities and reported ultrasonic velocities. A considerable decrease in attenuation with frequency was observed in the investigated frequency range, with the value at high frequency ap­ proaching the classical attenuation. The results are in good agreement with Mountain's theory of a single relaxation time. The relaxation time of the bulk viscosity coefficient was calculated to 1.2×10-10S.

scholarly journals Extraction of γ-Alumina from Low-Cost Kaolin

Resources ◽  
2018 ◽  
Vol 7 (4) ◽  
pp. 63
Author(s):  
Khalil Ibrahim ◽  
Mohammad Moumani ◽  
Salsabeela Mohammad
Keyword(s):  
Low Cost ◽  
Morphological Properties ◽  
X Ray Diffraction ◽  
X Ray ◽  
Aluminum Metal ◽  
Alumina Particles ◽  
Two Stages ◽  
Method Of Extraction ◽  
Microcrystalline Powder ◽  
Made In

A combined process is proposed for the utilization of local kaolin to produce alumina particles. The applied process is made in two stages: calcination at 700 °C with sodium chloride and leaching with sulfuric followed by hydrochloric acids. The optimal extraction efficiency can be obtained when the conditions are as follows: leaching temperature is at 140 °C, leaching time is 3 h 45 min and concentration of sulfuric acid is 40 wt.%. The results show that the purity of alumina reaches 79.28%, which is suitable for the production of aluminum metal. It is evident that this method of extraction of alumina from the kaolin ash is practical and feasible. The structural and morphological properties of the calcined microcrystalline powder was characterized by X-ray diffraction and scanning electron microscope (SEM).

Positioning the Tata Nano (B)

2017 ◽  
pp. 1-2
Author(s):  
Alice M. Tybout ◽  
Natalie Fahey
Keyword(s):  
Production Capacity ◽  
Frame Of Reference ◽  
Product Launch ◽  
Limited Capacity ◽  
Brand Positioning ◽  
Decision Point ◽  
Safety Issues ◽  
Indian Consumers ◽  
Two Stages ◽  
Made In

The case focuses on positioning a new brand, the Tata Nano. The car has been widely publicized as the world's cheapest car at Rs.1 lakh. Students must consider the gap between the ultimate target, the huge emerging middle class of Indian consumers, and the limited capacity and distribution available in choosing a target. They also must select between alternative competitive frames and the various points of difference they highlight. The case unfolds in two stages. The first decision point is in 2009, at the launch of the time of the product launch. The second decision point is 18 months later, after production capacity has increased and some product safety issues have arisen.The primary goal of the case is to illustrate the choices made in developing a strong brand positioning and the interrelationship between these choices. Students select a target and an appropriate competitive frame of reference and point of difference for that target and summarize these elements in a positioning statement. The case also highlights importance of making promotion and distribution decisions that are consistent with the positioning.

Suppression of Static Electrification of Insulating Oil for Large Power Transformers

1982 ◽  
Vol PAS-101 (11) ◽  
pp. 4272-4280 ◽  
Author(s):  
M. Yasuda ◽  
K. Goto ◽  
H. Okubo ◽  
T. Ishii ◽  
E. Mori ◽  
...  
Keyword(s):  
Power Transformers ◽  
Large Power ◽  
Insulating Oil ◽  
Static Electrification
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