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In this paper, micro-stack insulators with different ratios of insulator-to-metal (I/M) and embedded micro-stacks are studied using nylon as an insulating layer and conductive silver adhesive applied as a conductive layer. The electric field of insulators with a micro-stack structure is simulated. The results show that the electric field strength decreases and the dielectric strength improves near the cathode triple junction following an increase of the I/M ratio when the micro-stack insulators have the same conductive layers. The optimal ratio is found to be 0.61 at which point the dielectric strength increases by 2.1 times. In addition, the dielectric strength of insulators was compared while the surface has been ground along two different directions respectively. the result was found to be better when the surface is polished along the Y axis direction than X axis. The experimental results can provide a technical reference for the preparation, structural design and mechanism exploration of the micro-stack insulators. [ABSTRACT FROM AUTHOR]

This paper presents a rotor shape multi-level-objective optimization designed to reduce the mechanical stress distribution in the rotor core of a double-stator permanent magnet synchronous motor. The second objective is weight minimization performed via a response surface methodology with a uniform precision central composite design function. The optimal operation point, with a substantial population size, is reached using a Monte Carlo algorithm on the fitted model. The goodness-of-fit for the model is evaluated based on the modified Akaike information criterion and the Bayesian information criterion with a linear regression approach. To achieve these goals, a multi-level design procedure is proposed for the first time in machine design engineering. All the electromagnetic forces of the machine, such as normal, tangential, and centrifugal forces, are calculated using three-dimensional transient finite element analysis. The outcome of the proposed rotor core optimization shows that the finalized shape of the studied core has significantly smaller weight and mechanical stress, while the electromagnetic performance of the machine has remained consistent with a pre-optimized machine. [ABSTRACT FROM AUTHOR]

This paper utilizes a Pareto-based, three-dimensional (3-D) analysis to identify complete and partial shading of photovoltaic (PV) systems for a complicated urban environment, where unusual shape of PV and installation topology is studied. The Pareto optimization attempts to minimize losses in a certain area with an improved output energy and without compromising the overall efficiency of the system of which the nominal operating cell temperature (NOCT) for a glass/glass-module is considered as a significant parameter. The system is referenced to the environment based on IEC61215 via a closed-circuit and resistive load to ensure the module operates at the maximum power point. A maximum power point tracking controller is enhanced with an advanced perturb and observe algorithm to maintain the PV operating point at its maximum output under various working conditions. The most cost-effective design of the PV module is achieved via optimizing installation parameters such as tilt angle, pitch, and shading to improve the energy yield. The parameter settings and suitability of the design are also determined based on the reduced amount of CO2 emissions. An experimental investigation has been carried out to verify the 3-D shading analysis and NOCT technique for both open-circuit and grid-connected PV modules. [ABSTRACT FROM AUTHOR]

In this paper, seven groups of sheet insulation for use in liquid nitrogen immersed power transformers have been tested under three different standard electrodes from ASTM D149-97a. The seven groups consist of three different types of paper/film, nonadhesive Kapton 100 HN (Kapton), THERNOMID 14.20 paper (NMN), and Nomex 410 paper (Nomex). The porous paper, Nomex 410, is found to have ac dielectric strength of 62–68 kV/mm, which is likely to be independent from its thickness. The nonporous film, Kapton, shows the dielectric strength of 288 kV/mm, whereas NMN paper has a dielectric strength of 74–78 kV/mm, larger than Nomex with similar thickness. Liquid nitrogen gaps near the triple junction of electrodes as well as liquid nitrogen pockets between the fibers are the main sources of partial discharge (PD) for NMN and Nomex. For Kapton, PDs are more likely to occur in the cavities filled with liquid nitrogen, either on the surface of the electrode or around the impurities on the surface of the film. Electrodes with a small stressed volume are more appropriate for dielectric tests of thin paper/film insulation, such as Kapton, due to the lower influence of cavities on the electrode surface. In contrast, electrodes with a large stressed volume and uniform electric field distribution are suitable for the papers such as Nomex and NMN. [ABSTRACT FROM AUTHOR]

This paper studies a dual-level response surface methodology (DRSM) coupled with Booth's algorithm using a simulated annealing (BA-SA) method as a multiobjective technique for parametric modeling and machine design optimization for the first time. The aim of the research is for power maximization and cost of manufacture minimization resulting in a highly optimized wind generator to improve small power generation performance. The DRSM is employed to determine the best set of design parameters for power maximization in a surface-mounted permanent magnet synchronous generator with an exterior-rotor topology. Additionally, the BA-SA method is investigated to minimize material cost while keeping the volume constant. DRSM by different design functions including mixed resolution robust design, full factorial design, central composite design, and box-behnken design are applied to optimize the power performance resulting in very small errors. An analysis of the variance via multilevel RSM plots is used to check the adequacy of fit in the design region and determines the parameter settings to manufacture a high-quality wind generator. The analytical and numerical calculations have been experimentally verified and have successfully validated the theoretical and multiobjective optimization design methods presented. [ABSTRACT FROM AUTHOR]

It is crucial for the successful application of high-temperature superconducting (HTS) power transformers that they are able to survive under abnormal operations, such as a short-circuit fault. Modeling, based on the design of a four-winding three-phase HTS power transformer, suggests severe boiling will occur on the surface of the winding during a short-circuit fault and will jeopardize the turn-to-turn insulation of the HTS power transformer. In this paper, a turn-to-turn insulation breakdown experiment platform involving the introduction of boiling on the surface of electrode has been built. Nomex 410 paper, one of the candidates for turn-to-turn insulation in the design of the HTS power transformer, was tested. The characteristics of dielectric strength of Nomex 410 in three different thicknesses (0.13, 0.18, and 0.25 mm) have been investigated, without boiling, as well as under different boiling situations, in an open bath of liquid nitrogen. The voltage application methods applied during both experiments test the electrical breakdown of Nomex 410 under a dynamic situation. The experiment results show that when under film boiling, compared to the test results for nucleate boiling, the dielectric strength of Nomex 410 paper decreases by approximately 38% of the value when no boiling is involved. Moreover, it is verified that the presence of an electric field accelerates the heat transfer between the liquid nitrogen and the heated electrode. [ABSTRACT FROM PUBLISHER]

A new 15-kVA, 230-230 V, high-temperature superconducting, partial-core transformer has been designed, built, and tested. The transformer utilizes a unique core design called partial core, consisting of a central laminated slug of core steel only. The windings are layer wound with first-generation Bi2223 HTS. In part 1 of this paper, a model is used to predict the performance of the transformer as well as the ac losses of the HTS. In this part, a series of electrical tests was performed on the transformer, including open circuit, short circuit, resistive load, overload, ac withstand voltage, and fault ridethrough tests. The test results are compared with the model. The transformer was found to be 98.2% efficient at rated power with 2.86% voltage regulation. [ABSTRACT FROM AUTHOR]

A new 15-kVA, 230–230 V, high-temperature superconducting (HTS), partial-core transformer has been designed, built, and tested. The transformer utilizes a unique core design termed partial core, consisting of a central laminated slug of core steel only. The windings are layer wound with first-generation Bi2223 HTS. A model was developed to predict the performance of the transformer as well as the ac losses of the HTS and is presented in this paper. Part 2 of this paper presents the construction details and experimental results. [ABSTRACT FROM AUTHOR]

An experimental high temperature superconducting transformer has been designed and built using Bi2223 HTS tape. The transformer is unique in that the magnetic circuit is comprised of air and a silicon steel partial core. Electrical tests were performed on the transformer and it was found to be 98.6% efficient at full load. The transformer failed during a full load endurance run and an investigation was carried out to determine the cause of the failure. The cause was believed to be from operating the HTS windings close to critical conditions. Presentation of the failure details will be of use to other researchers who are building HTS transformers. [ABSTRACT FROM AUTHOR]

Corrections to “The Dielectric Strength of Nomex 410 Paper in Liquid Nitrogen under Boiling Situations” [ABSTRACT FROM AUTHOR]