다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

https://opus.lib.uts.edu.au/bitstream/10453/114834/4/OCC-90253_AM.pdf

A review of clustering techniques and developments

Time--frequency feature representation using energy concentration: An overview of recent advances

Requirement of green supply with higher quality has been consumers’ demand around the globe The electrical power system is expected to deliver undistorted sinusoidal rated voltage and current continuously at rated frequency to the consumers This paper presents a comprehensive review of signal processing and intelligent techniques for automatic classification of the power quality (PQ) events and an effect of noise on detection and classification of disturbances It is intended to provide a wide spectrum on the status of detection and classification of PQ disturbances as well as an effect of noise on detection and classification of PQ events to the researchers, designers and engineers working on power quality More than 150 research publications on detection and classification techniques of PQ disturbances have been critically examined, classified and listed for quick reference

A critical review of detection and classification of power quality events

Assessment of insulation condition by sensing and subsequent analysis of oil-impregnated paper response at periodic intervals is necessary for reliable operation of transformers. Sensing frequency domain insulation response requires the application of either a sinusoidal excitation voltage (over a wide range) or a custom excitation waveform. This not only requires a specially designed variable-frequency variable-amplitude excitation voltage source but also makes measurement practically problematic. Measurement of low-frequency data is time-consuming and the data tends to get affected by field noise. In comparison, a simpler and cheaper alternative is the analysis of time-domain insulation response. This involves the measurement of low amplitude polarization and depolarization current. A pico-ammeter or Electrometer is generally used for this purpose. The available interpretation scheme of time domain response sensed using Electrometer does not consider the de-trapping charge’s polarity. The result presented in the paper shows that such an assumption inadvertently leads to inaccurate diagnosis. This, in turn, generates doubt regarding the current sensing capability of the Electrometer involved. In the present work, a better interpretation scheme of the data sensed by the Electrometer is discussed. The significance and influence of de-trapped charge polarity on polarization and depolarization currents are investigated. The analysis is tested on data collected from real-life in-service power transformers.

Influence of De-Trapped Charge Polarity in Sensing Health of Power Transformer Insulation

Leakage current pattern and its harmonic content are widely known to be excellent monitoring indices for condition assessment of overhead line insulators. Whenever there is a change in the contamination severity on the insulator surface, a corresponding change in the leakage current is observed. Traditionally, it has been assumed that the changes in leakage current pattern are entirely due to the changes in surface condition of insulators. However, in real-time online monitoring, the system voltage and its harmonic content will also have a certain effect on the leakage current pattern. Changes in the harmonic content of system voltage may also produce changes in the leakage current pattern. This may lead to incorrect interpretation of the obtained results where systems are prone to harmonic distortions. In such cases, there is no way of knowing whether the change in leakage current pattern is entirely due to changes in surface condition of insulators or on account of harmonics in the applied voltage. Keeping this in mind, this work investigates for the first time the effect of presence of harmonics in voltage waveform on the leakage current pattern in overhead insulators. The purpose of this paper is to present the preliminary results on the degree of influence of voltage harmonics on the leakage current pattern, and demonstrate the importance of more detailed research on the topic.

Investigations on the effect of voltage harmonics on leakage current for condition monitoring in insulators

Various types of insulation models with time-invariant parameters are available in the literature. Depending on the aging sensitive performance parameters to be evaluated, different models need to be employed (e.g. XY model for oil and paper-conductivity, conventional Debye model (CDM) for paper-moisture and tanδ). While the XY model cannot be used for estimating paper-moisture directly, analysis based on CDM parameter becomes dependent on its branch parameters, which are non-unique. These factors lead to either incomplete or ambiguous insulation diagnosis. These problems are resolved using the proposed new insulation model containing unique time-varying branch parameters. Another major advantage of the proposed model is that it can be used to evaluate a host of performance parameters (like paper-conductivity, oil and paper-moisture, dielectric loss) thus giving a complete picture of the insulation concerned. The application of the proposed model is also tested on data collected from several real-life power transformers.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-smt.2018.5673

Effective analysis of time-domain dielectric response for reliable diagnosis of power transformer insulation using statistical parameter evaluated from time-varying model

Sivaji Chakravorti

Papers

Influence of De-Trapped Charge Polarity in Sensing Health of Power Transformer Insulation

Investigations on the effect of voltage harmonics on leakage current for condition monitoring in insulators

Effective analysis of time-domain dielectric response for reliable diagnosis of power transformer insulation using statistical parameter evaluated from time-varying model

Sphere or Cylinder in Uniform External Field

Ageing of DC conduction in thermally aged oil-impregnated pressboard