583 research outputs found

    Technical and vocational skills (TVS): a means of preventing violence among youth in Nigeria

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    Technical and vocational skills are an important tool for reducing violence among youth, especially in Nigeria, who face security challenges due to different kinds of violence. This paper focusses on the policies and programmes intended to provide youth with skills that can help them improve their life instead of engaging in violence. The paper also studies youth participation in violence. The study shows that youth in Nigeria participate in violence because of unemployment and economic pressure. These youth are mostly from poor families and are mostly used by others to achieve their own unlawful ambition. The data were collected from various secondary sources such as textbooks, journals and conference papers that were carefully reviewed. The results obtained from the literature revealed that youth are not committed, sensitised and mobilised to taking advantage of the opportunities available to them. The results also revealed that almost all the programmes meant to provide youths with skills have failed. Poverty alleviation programmes established to create jobs, self-employment and self-reliance have been unsuccessful. Therefore, alternatives must be provided to help the younger generations. Based on the literature reviewed, the paper discusses related issues and outcomes and ends with recommendations to improve the situation

    Evaluation of Lightning Impulse Test by Frequency Response Analysis

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    In this work are presented the basis for improving the interpretation of transformer lightning impulse test and the development of a graphical user interface system, which allows comparisons of time domain data and frequency response. The frequency response is obtained from deconvolution of voltage and neutral current records. A quantitative comparison of frequency response is performed using the techniques applied to displacement detection through Frequency Response Analysis, such as correlation and spectral deviation. The system is implemented using 8 bit digitizers to acquire the voltage and neutral current records. The quantization error and reliability of the frequency response obtained is handled through the use of the coherence function and tolerance bands. The system is thoroughly tested applying a lightning impulse test to a dry type distribution transformer, simulating an interdisc fault with a spark gap. Failure detection is confirmed

    Diagnostic methods of frequency response analysis for power transformer winding a review

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    Abstract: Monitoring and diagnosis of power transformers in power systems have been investigated and discussed for the past decades. Earlier detect power transformer winding failures is recommended for both manufacturing process and also for power system operators. One of the most powerful and accurate tool for sufficient winding deformation detection is considered Frequency Response Analysis (FRA) among other diagnostic methods. In this paper a review of diagnostic methods of FRA for power transformer winding are presented. Different methods of transformer winding diagnosis, with their benefits and drawbacks where investigated. Moreover, possible windings failures, diagnostic methods of FRA in Off-line and On-line power transformers, detailed advantages and disadvantages of two major types of FRA are presented. The paper was able to show that some uncertainties have not been eliminated completely

    Frequency Response Analysis Using High Frequency Transformer Model

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    FAULT DETECTION USING FRA IN ORDER TO IMPROVE THE AGING MODEL OF POWER TRANSFORMER

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    Power transformers are constantly exposed to mechanical, thermal and electrical stresses during operation. In this paper, the authors propose an improved aging model of power transformers by adding the impact of mechanical deteriorations. In the current practice, the mechanical deformation and dislocation of the windings and core are not sufficiently distinguished as components that influence the aging of the transformer. Hence, the current aging model was expanded with a functional block that contains several typical failures in order to emphasize their impact on the lifetime of transformers and their aging as well.  The authors used the Frequency Response Analysis (FRA) method for the fault detection and location of the mechanical deformations of its active parts. The correlation function is used to determine the level of the detected failure. All presented test results are obtained in real exploitation conditions

    Characterization of Power Transformer Frequency Response Signature using Finite Element Analysis

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    Power transformers are a vital link in electrical transmission and distribution networks. Monitoring and diagnostic techniques are essential to decrease maintenance and improve the reliability of the equipment.This research has developed a novel, versatile, reliable and robust technique for modelling high frequency power transformers. The purpose of this modelling is to enable engineers to conduct sensitivity analyses of FRA in the course of evaluating mechanical defects of power transformer windings. The importance of this new development is that it can be applied successfully to industry transformers of real geometries

    A review of transformer FRA measurement and diagnosis techniques

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    Frequency Response Analysis (FRA) is a successful technique to detect mechanical damage in power transformers with greater sensitivity than other measurements. The SFRA method is commonly used today and requires a benchmark FRA measurement for comparative diagnostic methods. The use of numerical indices to quantify differences in two FRA signatures is described. It is important to understand the importance of understanding the physical meaning behind the frequency responses of windings through modelling and simulation

    A review of transformer FRA measurement and diagnosis techniques

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    Frequency Response Analysis (FRA) is a successful technique to detect mechanical damage in power transformers with greater sensitivity than other measurements. The SFRA method is commonly used today and requires a benchmark FRA measurement for comparative diagnostic methods. The use of numerical indices to quantify differences in two FRA signatures is described. It is important to understand the importance of understanding the physical meaning behind the frequency responses of windings through modelling and simulation

    Pembangunan dan penilaian sistem 'template' soal selidik berasaskan web (e-templete questionnaire)

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    Kajian ini dijaiankan bagi meninjau keboiehgunaan dan tahap mesra pengguna terhadap g-?e?77p/a/g soal selidik. Fokus utama kajian ini adaiah (i) menilai tahap keboiehgunaan <?-/<?/7?/?/<3/<? soal-selidik daiam pembangunan soal selidik secara atas talian sebagai instrumen penyeiidikan, (ii) menilai tahap keboiehgunaan g-Zgnzp/a/g soal selidik yang dibangunkan untuk proses pengumpuian data penyeiidikan, (iii) menilai tahap keselamatan g-fgwzp/a/e soal selidik yang dibangunkan, (iv) menilai tahap mesra pengguna g-Zg/wp/a/g, (v) menilai tahap keberkesanan g-fgnzp/a/g soal selidik dan (vi) menilai sama ada terdapat perbezaan yang signifikan di antara persepsi peiajar dan pensyarah terhadap tahap keberkesanan e-?g77zp/afe soal selidik berkenaan. Rekabentuk kajian yang dijaiankan adaiah berbentuk kajian tinjauan dan melibatkan kedua-dua kaedah kualitatif dan kuantitatif. Responden kajian ini terdiri daripada 10 orang pensyarah, 10 orang kakitangan am dan 30 orang peiajar yang terlibat dengan aktiviti penyeiidikan. Instrumen kajian yang digunakan adaiah borang soal selidik dan temubual. Kajian ini mengambil kira aspek keberkesanan g-re772p/a?g yang merangkumi tahap keboiehgunaan sistem berkenaan daiam pembangunan borang soal selidik secara atas talian, keboiehgunaan sistem daiam aspek pengumpuian data, tahap keselamatan data dan tahap mesra pengguna. Kajian ini menguji sama ada terdapat perbezaan persepsi peiajar dan pensyarah terhadap tahap keberkesanan g-Zgnzp/a/g yang dibangunkan. Hasil daripada kajian mendapati tahap keboiehgunaan daiam pembangunan soal selidik berada pada tahap tinggi iaitu dengan memperoleh skor min = 3.97 . Tahap keboiehgunaan untuk aktiviti pengumpuian data memperoleh skor min = 4.03. Manakala untuk tahap keselamatan skor min yang diperoleh adaiah 3.95. Bagi tahap mesra pengguna skor min yang diterima adaiah 3.85. Akhir sekali, tahap keberkesanan g-/g/Mp/a/rg memperoleh skor min 3.95. Kajian juga mendapati bahawa tidak terdapat perbezaan yang signifikan antara persepsi peiajar dan pensyarah terhadap g-/gHzp/a7g yang dibangunkan. Pembangun mencadangkan supaya laman web g-?gmp/a?g ini dapat dimumikan lagi dengan penambahan fungsi untuk menganalisis data. Ini kerana fungsi berkenaan tidak dapat dibangunkan

    Exploring Statistical Index Criteria for Transformer Frequency Response Interpretation

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    Large power transformers are considered as the most expensive assets in power system network after hydro generators. Therefore, monitoring of such equipment needs to take special attention. Frequency Response Analysis (FRA) is one of the efficient methods to examine the mechanical condition of the transformer without opening the transformer tank. FRA is a comparative method, where the measured response is compared to the reference fingerprints. Therefore, interpretation of the FRA results needs to be done by an expert in the field. To overcome this problem, so that untrained personnel would be able to use FRA for transformer condition monitoring the interpretation of the frequency response should be based on standard or on some criteria. In this study, various statistical indices for frequency response results interpretation will be introduced and evaluated. Frequency responses of single-phase 0.4-1kVA transformers and three-phase transformers up to 40kVA are interpreted by statistical indices. Outcome of each indicator is discussed and the most reliable ones for FR interpretation are suggested. The simulation of inter-disk short circuit was performed by the rheostat connected in parallel with the winding of transformer. The voltage taps of the transformers were used in order to have the access to different percentage of the transformer winding. With the help of different voltage taps and different resistances in parallel, the two levels of critical values were found and advised to use
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