1,720,987 research outputs found
Partial discharge phase and amplitude distribution and life of insulation systems fed with multilevel inverters
No full textThis paper presents an investigation on the effect of the number of levels and voltage magnitude of a multilevel power electronic supply on reliability of insulation systems. Particular attention is given to partial discharge, PD, behavior, referring to organic (Type I) insulating materials used for rotating machines fed by variable source inverters, VSI. As described in standard IEC 60034-18-41 and 42, repetitive voltage impulses, as those generated by pulse-width modulation, PWM, supply, can incept PD due to uneven voltage distribution in windings and transient overvoltage, which would not occur with an AC power supply. The presence of PD will affect drastically reliability, and thus life, of electrical insulation, to an extent which depends on their amplitude and repetition rate. The effect of number of inverter levels and peak voltage on PD repetition rate and amplitude is modelled, validated by experimental data, and correlated to insulation aging rate, showing that increasing the number of levels is beneficial for insulation reliability and providing an analytical support to PD measurements under PWM
Type of Supply Waveform, Partial Discharge Behavior and Life of Rotating Machine Insulation Systems
No full textThis paper highlights the effects voltage supply waveform can have on partial discharge, PD, characteristics in insulation systems of rotating machines fed by power electronics drives. While standards allow both sinusoidal and repetitive voltage impulse waveforms to be used for insulation design and type tests, the dependence of PD on the voltage waveform implies that the machine design and performance can be affected significantly by the waveform. Partial discharge inception voltage, partial discharge patterns and insulation life are, in fact, dependent on the type of test waveform. This can affect significantly the design of machine insulation system
Noise rejection and partial discharge identification in PDIV tests of insulated wires under repetitive impulse supply voltage
No full textPartial discharge (PD) detection is a fundamental test for the design and diagnosis of insulation systems, particularly organic materials which must operate throughout their whole life without PD. The measurement of Partial Discharge Inception Voltage (PDIV) and Repetitive Partial Discharge Inception Voltage (RPDIV), the latter defined for power electronic-type supply, is therefore a key issue for the design and qualification tests of Type I insulation system of rotating machines fed by power converters. While experience and technology for PD inception measurements under sinusoidal voltage supply is well established, the same does not hold under repetitive-pulse voltage waveforms, such as those provided by inverters. In addition, electromagnetic noise generated by electronic switch commutation can overlap with PD pulses signals and this is even more cumbersome when fast rise-time components are employed, such as GaN or SiC semiconductors. Moreover, this is also the condition which is the most stressful for stator wire insulation. This work investigates methods to detect PD pulses on enameled wires, rejecting noise efficiently, under repetitive impulsive voltages with different rise times, from 60 ns to 1000 ns. The proposed techniques can be implemented to achieve un-supervised noise rejection, which would be an important goal for both off-line and on-line PD testing
Self-Assessment of Health Conditions of Electrical Assets and Grid Components: A Contribution to Smart Grids
Full text linkBroadening the concept of smart grid to include bi-directional interactions between grid and asset electrical components as regards their health conditions would help optimizing maintenance and operation actions from asset/grid management side. However, as long as data processing from diagnostic tools requires long and costly expert time, there is no real chance that the knowledge and technology developed in the field of condition monitoring can become broadly available for grid smart management. This article presents algorithms able to automate the acquisition of health information from electrical asset components. Referring to partial discharges, which are associated with the most harmful insulation aging factor, an innovative technique able to reject noise and thus make automatic partial discharge recognition possible, is proposed and its validity assessed. The information from partial discharge measurement, and other diagnostic quantity monitored is translated into a simple and straightforward indication of component health. This assessment can be automatic, dynamic and continuously updating during operation, thus making feasible an effective time-based condition maintenance approach. The outcome of the proposed approach is to contribute keeping asset reliability at a specified level, minimizing disastrous outages and increasing the return of investment. This benefits also optimal electrical component operation and power flow
Noise Rejection and Detection of Partial Discharges under Repetitive Impulse Supply Voltage
Full text linkPartial discharge (PD) detection is a fundamental tool for the design and diagnosis of insulation systems, particularly organic materials that must operate throughout their life without PD. While the methods for PD measurements under sinusoidal supply voltage are well-established, the same does not hold under repetitive-pulse voltage waveforms, such as those provided by inverters. Electromagnetic noise generated by electronic switch commutation in inverters can overlap with PD pulses, making it difficult to measure, separate from noise, and identify PD. This is particularly more cumbersome when fast rise-time switches are employed. To address these issues, this paper investigates methods to detect PD pulses on enameled wires under repetitive impulsive voltages with different rise times of 60, 500, and 1000 ns, proposing techniques which allow separation of PD from noise even when they overlap in time and frequency domains. This paper employs a time-domain approach using standard deviation curve acquired from a set of measurements to discriminate PD from repetitive commutation disturbance. These techniques can be implemented to achieve unsupervised noise rejection, which would be an important goal for both offline and online PD testing. The proposed approach is validated successfully through tests carried out on a low-voltage motor
An approach to insulation condition monitoring and life assessment in emerging electrical environments
No full textDistributed generation, dc transmission and distribution, and power electronics for ac/dc/ac conversion bring the advantages of increased control and flexibility in electric power management. These advantages also introduce challenges that must be managed. An electrical environment where voltage is not anymore strictly sinusoidal implies that a new approach for the design and maintenance of electrical insulation systems has to be devised. Non-sinusoidal voltage supply often causes increased failure probability and, thus, reduced reliability and life of an electrical asset. This research addresses the implications of the transient and steady waveform distortion introduced by power electronic systems and dc supply, for which the electrical insulation was designed and tested through consolidated criteria based on sinusoidal voltage supply. Based on condition monitoring, a health index definition is proposed, which allows the condition of the insulation of an electrical apparatus to be assessed as a function of operation time, and, based on the aging and life models, the evaluation of maintenance actions and of the feasibility and extent of life extension plans to be carried out
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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