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, non-adhesive Kapton 100HN (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 non-porous 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.
Multiobjective Design Optimization Using Dual-Level Response Surface Methodology and Booth's Algorithm for Permanent Mag...Published: 01 June 2018 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Energy Conversion
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.
According to our previous research on the dielectric strength of Nomex T410 paper under a horizontal turn-to-turn electrode system, a significant decrease by approximately 38% of the dielectric strength was found after the introduction of film boiling. In this paper, a wide range of sheet insulation samples has been tested under a turn-to-turn electrode system in vertical arrangement, more practical to the real design of high-temperature superconducting (HTS) power transformers. Samples from three different types of paper (NMN, Nomex and Kapton) have been investigated under a static situation with no boiling introduced. In addition, their dynamic dielectric characteristics under different levels of electric stress have also been tested by introducing a transient thermal stress. The experiment has been conducted in open bath liquid nitrogen (77K) as well as in sub-cooled liquid nitrogen (67K). Both of the tests are conducted under one atmospheric pressure. The result shows that all samples have enhanced dielectric performance when immersed in the sub-cooled liquid nitrogen. Moreover, the Kapton film is found to always have the best dielectric performance. However, its poor impregnation of liquid nitrogen largely affects its dielectric strength, especially at 77K. When compared to Nomex paper with a similar thickness, the NMN paper is better due to its non-porous structure.
Load identification of different Halbach-array topologies on permanent magnet synchronous generators using the coupled f...Published: 01 January 2018 by Elsevier BV in Electric Power Systems Research
A COMPARATIVE STUDY OF QUASI-FEA TECHNIQUE ON IRON LOSSES PREDICTION FOR PERMANENT MAGNET SYNCHRONOUS MACHINESPublished: 01 January 2018 by EMW Publishing in Progress In Electromagnetics Research C
This paper utilizes a Pareto-based, three-dimensional (3-D) analysis to identify complete and partial shading of photovoltaic (PV) systems for an 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 (MPPT) controller is enhanced with an advanced perturb and observe (P&O) 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.
This research 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 (RSM) with a uniform precision central composite design (UP-CCD) function. The optimal operation point, with a substantial population size, is reached using a Monto Carlo algorithm on the fitted model. The goodness-of-fit for the model is evaluated based on the modified Akaike information criterion (AICc) and the Bayesian information criterion (BIC) 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 3-D transient finite element analysis (FEA). 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.
Optimal Pole Number for Magnetic Noise Reduction in Variable Speed Permanent Magnet Synchronous Machines with Fractional...Published: 01 January 2018 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Transportation Electrification
Iron Loss Prediction Using Modified IEM-Formula during the Field Weakening for Permanent Magnet Synchronous MachinesPublished: 05 December 2017 by MDPI in Machines
During field weakening operation time (FWOT), the total iron loss rises and affects the accuracy of loss prediction and efficiency, especially if a large range of FWOT exists due to a large voltage drop that was rooted from the resistance of the used material. Iron loss prediction is widely employed in investigations for a fast electrical machine analysis using 2D finite element analysis (FEA). This paper proposes harmonic loss analytically by a steady-state equivalent circuit with a novel procedure. Consideration of skin effects and iron saturation are utilized in order to examine the accuracy through the relative error distribution in the frequency domain of each model from 50 to 700 Hz. Additionally, this comparative study presents a torque-frequency-field density calculation over each single term of the modified institute of electrical machines formula (IEM-Formula). The proposed analytical calculation is performed using 2D FEA for a classic and modified IEM-Formula along with experimental verifications on a surface-mounted permanent magnet synchronous generator (PMSG) for a wind generation application.
Iron Loss Prediction Using Modified IEM-Formula during the Flux Weakening for Permanent Magnet Synchronous MachinesPublished: 24 October 2017 by MDPI (Preprints) in ENGINEERING
During flux weakening operation time (FWOT), the total iron loss rises and affects the accuracy of loss prediction and efficiency especially if a large range of FWOT exists. Iron loss prediction is widely employed in investigations for a fast electrical machine analysis using 2-D FEA. This paper studies harmonic loss analytically by a steady-state equivalent circuit. Consideration of skin effects and iron saturation are utilized in order to examine the accuracy through the relative error distribution in the frequency domain of each model from 50 to 700 Hz. Additionally, this comparative study presents a torque-frequency-flux density calculation over each single term of the modified IEM-formula. The analytical calculation is performed using 2-D FEA for a classic and modified IEM-formula along with experimental verifications on a surface-mounted PMSG for a wind generation application.
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.
Tongan Schools go Solar; Is it Possible to Deliver Development Projects with Cost-Effective Partnerships?Published: 31 October 2013 by MDPI AG in The 3rd World Sustainability Forum
In 2012 a group of volunteering University of Canterbury (UC) staff, students and alumni worked in partnership with the Kingdom of Tonga Ministry of Education and Training (MET), Tongan State-owned enterprise Tonga Power Ltd (TPL) and local contractors, to design, procure and install photovoltaic (PV) systems of 8 kW peak in five Tongan High Schools. The project was funded by the New Zealand Ministry of Foreign Affairs and Trade (MFAT) in an effort to assist Tongan high schools to reduce their relatively expensive utility related costs and to enable schools the financial freedom to invest in educational resources. The project was implemented in a unique multi party Pubic Private Non Profit Partnership model to utilise the resource pool of UC and provide practical academic opportunities to university students while providing overseas development assistance to Tonga. This paper presents the planning and execution of this project, and discusses the areas of challenges, opportunities, success and failure by revisiting the unique partnership model, in concept and in practice. To understand schools’ expectations and perspective from a beneficiary point of view, staff and students from each school were interviewed during the installation. Subsequently, staff from each school were surveyed as part of a monitoring and evaluation study. Analysis of stakeholder interviews and recipient schools' survey results are presented and discussed with recommendations to execute similar multi-party sustainable development projects effectively, particularly in small island developing countries.
This paper presents a proof of concept and equivalent circuit analysis of a cascade arrangement of tunable HV testing transformers intended for field use. The transformers use a partial core with air completing the flux path and are tuned to resonate with insulation capacitance. This minimises the power drawn from the supply and the size and weight of the transformer. A prototype set of transformers were built to validate the model. Each transformer was modelled as a set of coupled inductors to determine the input impedance frequency response. Good agreement is shown between the modelled and measured input impedance. The inclusion of core loss resistance was shown to significantly increase the accuracy of the cascade model.
A 15-kVA High-Temperature Superconducting Partial-Core Transformer—Part II: Construction Details and Experimental Testin...Published: 01 January 2013 by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Power Delivery
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.
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.