فیلترها/جستجو در نتایج    

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متن کامل


نویسندگان: 

SUJA S. | JEROME J.

اطلاعات دوره: 
  • سال: 

    2008
  • دوره: 

    7
  • شماره: 

    2
  • صفحات: 

    153-158
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    307
  • دانلود: 

    0
چکیده: 

This paper presents a new method based on the wavelet packet transform for the analysis of harmonics in power systems. The algorithm can simultaneously measure the rms value of current, voltage and power using wavelet packets transform. The advantage of the wavelet packets transform is that it can decompose a power signal into uniform frequency bands. This decomposition into uniform frequency bands helps for the identification of harmonic components and measure of harmonic parameters. The algorithm is validated using simulated waveforms from the full wave inverter bridge circuit.

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اطلاعات دوره: 
  • سال: 

    2022
  • دوره: 

    18
  • شماره: 

    4
  • صفحات: 

    85-97
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    31
  • دانلود: 

    0
چکیده: 

The progressive application of non-linear loads in distribution systems (DS) increases current harmonics flow in DS's apparatuses, especially distribution transformers (DTs). Since DTs' operating temperature rises due to the harmonics flow, their loading should be reduced such that the hot spot temperature (HST) is preserved under its permissible value. This means that DTs' available capacity is influenced by load harmonic content. In this paper, a novel formulation for DTs' failure rate in the presence of harmonics is presented as a function of load harmonic contents. Using the suggested equivalent failure rate, DTs' available capacity in harmonic polluted DS is mathematically formulated. Additionally, the presence of the harmonic increases the HST, leading to DTs' aging acceleration. Therefore, the impact of harmonic components on DTs' aging is arithmetically modeled. To evaluate the efficacy of the suggested reliability model, it is applied to three distinct DTs having respectively industrial, commercial, and residential loads. The obtained results indicate that the available capacity of DTs with the same rated capacity would be different regarding to their load harmonic contents. On the other hand, it is comprehended from the achieved results that the aging acceleration factor (Faa) of the DTs increases owing to their load harmonic contents.

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نویسندگان: 

KINGSLEY C.U. | RAMIZI M. | AINI H. | AZAH M.

اطلاعات دوره: 
  • سال: 

    2004
  • دوره: 

    3
  • شماره: 

    2
  • صفحات: 

    111-116
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    349
  • دانلود: 

    0
چکیده: 

One of the power quality concerns that have received most attention is the problem of harmonics which are generated by widely dispersed single phase nonlinear loads.Such loads cause harmonic distortion of voltages and currents in a power distribution system. In order to fully understand the problem of harmonic distortion, an effective means of identifying the harmonic patterns generated by different types of nonlinear loads is considered. This paper presents the application of fractal analysis for analyzing various harmonic current waveforms generated by typical nonlinear loads such as personal computer, fluorescent lights and uninterruptible power supply. The fractal technique provides both time and spectral information of the nonlinear load harmonic patterns. The analysis results shows that the various harmonic current waveforms can be easily identified from the characteristics of the fractal features. This investigation proves that the fractal technique is a useful tool for identifying harmonic current waveforms and forms a basis towards the development of the harmonic load recognition system.

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نویسندگان: 

PISHVAEE M. | FATHI S.H. | GHARAHPETIAN G.B.

نشریه: 

AMIRKABIR

اطلاعات دوره: 
  • سال: 

    2006
  • دوره: 

    17
  • شماره: 

    64-A
  • صفحات: 

    55-61
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    251
  • دانلود: 

    0
چکیده: 

This paper presents the study of shunt active filters which inject compensating current into the network with time delays. It is shown that the performance of the filter is influenced by the variations of the nonlinear load harmonic contents. Measurement results are obtained from several industrial and domestic loads. The samples of the load currents are analyzed by fast Fourier transform. The delay in the compensating current injection is simulated by Matlab software and harmonics of the source current after compensation are compared with the standard permitted harmonic levels (IEEE 519). It is shown that the compensation is not completed for nonlinear loads and, in some cases, does not satisfy the standard requirements. Thus, it is concluded that before selecting a control strategy for the active filter (even, before selecting an active filter for compensation purpose), behavior of the nonlinear load must be studied and inspected from harmonic content variations point of view.

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نویسندگان: 

HOSSEINI S.H. | MOHAMMADI K.

اطلاعات دوره: 
  • سال: 

    2007
  • دوره: 

    3
  • شماره: 

    2
  • صفحات: 

    35-42
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    281
  • دانلود: 

    0
چکیده: 

Nowadays with increasing use of numerous nonlinear loads, voltage and current harmonics in power systems are one of the most important problems power engineers encounter.Many of these nonlinear loads, because of their dynamic natures, inject time-varying harmonics into power system. Common techniques applied for harmonics measurement and assessment such as FFT have significant errors in present of time-varying harmonics due to the time-windows applied. In this paper, a Kalman filter-based algorithm is developed and implemented for measuring time-varying harmonics. The efficiency of the proposed algorithm has been successfully tested in off-line mode by various computer simulations. Based on this algorithm, a prototype harmonic analyzer has been designed, fabricated and used for on-line harmonic monitoring and assessment studies. To assess the severity of time-varying harmonics, cumulative time indices that are computed in real-time using the output of the analyzer are proposed. In addition, new cumulative time curves for total harmonic distortion and individual harmonic distortions are presented.Also, an auto-synchronization algorithm is proposed to accompany the Kalman filter algorithm in order to eliminate the errors occurred due to the variations in the incoming signal frequency.

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اطلاعات دوره: 
  • سال: 

    2004
  • دوره: 

    19
تعامل: 
  • بازدید: 

    221
  • دانلود: 

    0
چکیده: 

THIS PAPER ANALYZES THE HARMONIC PERFORMANCE OF THYRISTOR CONTROLLED SERIES COMPENSATORS (TCSCS) IN POWER SYSTEMS AND PROPOSES AN EFFECTIVE METHOD FOR ITS CONTROL AND LIMITATION IN THE COMPENSATED LINE. THIS IS PERFORMED BY PROPER SELECTION OF TCSC ELEMENTS (CAPACITANCE AND INDUCTANCE) AND INTRODUCING A NEW METHOD FOR ADJUSTING ITS FIRING ANGLE SUCH THAT HIGH LINE LOAD ABILITY AS WELL AS LOW HARMONIC GENERATION IS ACHIEVED. FINALLY, A TCSC IS DESIGNED, MODELED, SIMULATED AND ANALYZED. THE MAIN CONTRIBUTION IS CONSIDERATION OF POWER QUALITY PHENOMENA AS WELL AS LOAD ABILITY IN THE TCSC CONTROL SCHEME.

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اطلاعات دوره: 
  • سال: 

    1399
  • دوره: 

    41
  • شماره: 

    4 (پیاپی 94)
  • صفحات: 

    1-10
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    345
  • دانلود: 

    140
چکیده: 

در این پژوهش نقش اثرات چند-الکترونی در تولید هماهنگ های مراتب بالا توسط برهم کنش لیزر فمتوثانیه با اتم آرگون و مولکول مونوکسید دی نیتروژن بررسی شده است. ابتدا اثر حضور بیش از یک الکترون در فرایند تولید هماهنگ ها مطالعه شده است. در این مطالعه مشاهده شد که حضور بیش از یک الکترون باعث افزایش شدت هماهنگ ها به ویژه در ناحیه فرکانس قطع می شود. این اثر در سیستم هایی که آخرین تراز پرشده آن ها تبهگن است، مشهودتر است. سپس اثر برهم کنش های همبستگی و تبادلی در تولید هماهنگ ها بررسی شده است. نتایج نشان می دهد که برهم کنش همبستگی به تنهایی تأثیر ناچیزی در فرایند تولید هماهنگ ها دارد، اما تأثیر هر دو برهم کنش تبادلی و همبستگی در این فرایند قابل توجه است. در واقع این تأثیر قابل توجه ناشی از برهم کنش تبادلی است، زیرا این برهم کنش 17% و 23% از انرژی کل اتم آرگون و مولکول مونوکسید دی نیتروژن را تشکیل می دهد. با در نظر گرفتن برهم کنش تبادلی-همبستگی برای آرگون و مونوکسید دی نیتروژن، شدت هماهنگ ها حدود یک مرتبه بزرگی کاهش و فرکانس قطع حدود 4-5 مرتبه هماهنگ افزایش می یابد.

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اطلاعات دوره: 
  • سال: 

    621
  • دوره: 

    15
  • شماره: 

    51 (English Special Issue)
  • صفحات: 

    15-24
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    15
  • دانلود: 

    0
چکیده: 

High Spatial and temporal variability of the tropospheric wet refractivity index, makes it difficult to present an accurate model for this variable. Up to now, Radiosonde stations data have been used for monitoring atmosphere parameters. Furthermore, because of the sparse distribution of radiosonde stations to monitor the lower levels of the atmosphere, the numerical weather models do not have enough accuracies for atmospheric parameters. Using the GPS tropospheric delay measurements and tomography approaches, the wet refractivity index can be estimated. In this research, three-dimensional and four-dimensional basis-function tomography is used to demonstrate the distribution of wet refractivity index of the troposphere. In this model, spherical cap harmonics are used for the horizontal distribution of the wet refractivity index, and empirical orthogonal functions are used for the vertical distribution of the index. In addition, temporal changes are considered by correlating the unknown coefficients using fourier series. The region of study is in the west California State, and the wet refractivity index is retrieved from the wet tropospheric delay measurements. To validate the results, radiosonde profiles were compared to the tomographically retrieved profiles. The results show that wet refractivity indices can be retrieved using functional models with RMSE about 2. 4 ppm till 3. 9 in the four-dimensional method. The comparisons show that the four-dimensional retrieved profiles show improvement up to 34 and 42 percentages in mid-day tomography epochs compared to the three-dimensional tomography results. Also it can be seen that in mid-night epochs, the three-dimensional tomography has higher accuracy compared to four-dimensional method because of low variation of wet refractivity indices.

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اطلاعات دوره: 
  • سال: 

    1385
  • دوره: 

    30
  • شماره: 

    ب-2
  • صفحات: 

    249-257
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    863
  • دانلود: 

    0
کلیدواژه: 
چکیده: 

این مقاله عملکرد هارمونیکی TCSC را در سیستم های قدرت بررسی کرده و یک روش مناسب جهت کنترل و محدود کردن هارمونیک ها در خط انتقال جبران شده با ادوات FACTS را ارایه می کند. این کار با اتنخاب صحیح المان های TCSC (خازن و سلف) و معرفی یک روش جدید برای تنظیم زاویه آتش طوری انجام می گیرد که حداکثر بارگذاری با تولید کم ترین هارمونیک ممکن انجام گردد. در نهایت یک TCSC نمونه طراحی، مدلسازی، شبیه سازی و مطالعه می شود. هدف اصلی این سیستم افزایش بارگذاری و درعین حال بهبود کیفیت توان می باشد که با روش کنترل مناسب TCSC پیاده گردیده است.

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اطلاعات دوره: 
  • سال: 

    1402
  • دوره: 

    13
  • شماره: 

    3
  • صفحات: 

    47-65
تعامل: 
  • استنادات: 

    0
  • بازدید: 

    161
  • دانلود: 

    14
چکیده: 

A B S T R A C TThe right to the city in urban development goes beyond the physical form and, at the same time, has a mental and social meaning, which has been popularized in planning theory and urban studies after its proposal by Lefebvre. This theory focuses on the residents and the distinctive features of the space and believes that the right to the city can only be formulated as the right to the evolved and renewed urban life. Based on descriptive-explanatory purpose, this research seeks to Spatially analyze the components of right to the city in Bandar Abbas. Therefore, after collecting 77 subjective and objective measures around the research components, the multi-criteria decision-making technique of COPRAS has been exploited to integrate the data in the ArcMap Tools. The findings show that in the current state of urban development in Bandar Abbas, the right to the city in all its aspects, the right to ownership, the right to participation and the right to difference for the residents have been weakened and ignored. A share of up to 20.7% of the city space, which is mainly directed to the wealthy neighborhoods and parts of the central areas of the city, as well as parts of new developments, the right to the city has been more manifested, and in about 19.8% of the city spaces. Mainly applicable to informal settlements and slums of the city, this right has been undermined and ignoredExtended AbstractIntroductionThe right to the city as a physical, mental and social concept seeks a fundamental change in dealing with urban planning and development issues, which has been popularized in planning theory and urban studies after its proposal by Lefebvre. This theory focuses on the residents and the distinctive features of the space and believes that the right to the city can only be formulated as the right to the evolved and renewed urban life. In other words, this theory is a call for the priority of the consumption value of the city against its exchange value, which can only be pursued through the analysis of urban issues in the framework of the "city space" metaphor in the right to the city. It is a fundamental change in the city to create opportunities and space for citizens to meet and achieve their needs. MethodologyFrom a descriptive-explanatory purpose, this research seeks to Spatially analyze the explanatory components of urban development in Bandar Abbas from the perspective of the right to the city. In this research, by collecting 77 subjective and objective measures, the COPRAS multi-criteria decision-making technique has been used to integrate data in the ArcMap environment. Citizens are the source of mental data, official documents and maps are the objective data, and experts are the relative weight of the criteria. It should be mentioned that to guarantee the validity of the content based on the guidance of supervisors and advisors, the collective opinion of university experts and the use of similar studies were exerted. The reliability of the questionnaire was also tested by Cronbach's alpha method, and the value of the alpha coefficient (0.866) indicates the high reliability of the questionnaire. Results and discussionThe findings show that in the current state of urban development in Bandar Abbas, the right to the city in all its aspects, including the right to possession, the right to participation, and the right to difference for the residents, has been weakened and ignored. A review of the findings shows that the social function of the city's real estate and land, with a coefficient of 0.136, followed by environmental justice, with a coefficient of 0.131, has the greatest impact on the urban development of Bandar Abbas. On the other hand, socio-Spatial justice in the process of taking over space, with a coefficient of 0.106, shows the lowest level of influence in the development of Bandar Abbas compared to other components of the right to the city. The results show that about 20% of the area of Bandar Abbas city is in a very unfavorable situation compared to the components of urban development based on the right to the city approach. These areas of the city are spaces where the residents' right to the city has been severely denied, and they are deprived of taking over the city space.In this regard, the results show that 20.7% of the city's space, mainly focused on wealthy neighborhoods, parts of the city's central areas, and parts of Mehr's housing, has the right to a greater manifestation of the city. The city's space is more in line with its residents. As shown in the Spatial distribution of the urban development components of Bandar Abbas based on the right to the city approach, the possession of space through the right to presence, the accessibility of residents to the opportunities and resources of the city, as well as the fair distribution of facilities and services play a decisive role in urban development. However, as the results show, it is the difference that gives meaning to the urban space, and therefore the space must provide the conditions for the city to play a role in meeting the needs of all city groups. The requirement of this role is the central position of the residents in making decisions about the city space, which is a unique way to realize the right to the city. ConclusionAs Brenner states, the right to the city is a call to create "cities for people, not for profit." In this definition, urban development is more than a physical thing and has a mental and social dimension at the same time. In terms of the right to the city, the right to possession, the right to participation, and the right to difference form the trinity of urban development and the guiding light of these three principles that determine the quality of a different city. Unfortunately, urban development in Bandar Abbas has weakened and denied residents' rights. The zoning resulting from the Spatial analysis shows that about 19.8% of the city's spaces, which mainly correspond to informal settlements and poor neighborhoods, this right has been weakened and ignored. From the theoretical aspect of the right to the city, this event originates from the space as an economic and physical thing exchanged in the market, not a consumption thing formed by the citizens and in social interaction with the space. FundingThere is no funding support. Authors’ ContributionAuthors contributed equally to the conceptualization and writing of the article. All of the authors approved thecontent of the manuscript and agreed on all aspects of the work declaration of competing interest none. Conflict of InterestAuthors declared no conflict of interest. Acknowledgments We are grateful to all the scientific consultants of this paper.

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