Multiphysics 3D modelling of ironless permanent magnet generators

Analytical method is widely used for the preliminary design and optimization of electrical machines. It has short calculation time and low computational cost (cost of simulation codes and supporting hardware), but the calculate result is normally considered to be not as accurate as finite element method (FEM). On the other hand, it is time-consuming to optimize machines with FEM if the optimization is not parallelized. Parallelizing optimization requires many licenses when commercial FEM codes are used, which can be very expensive. Ironless permanent magnet generator has large diameter and small aspect ratio, therefore, multiphysics approach is expected to be used for investigating the magnetic and thermal field. To address the above challenges, this paper presents a multiphysics modelling strategy for the design and optimization of ironless permanent magnet generators. Open-source codes are used to reduce the computational cost. A design example is presented to demonstrate the detail of this design method. This approach is expected to be used in super computer in the future, so that the calculation time can be largely reduced

Design Aspects on Winding of an MgB₂ Superconducting Generator Coil

AbstractGenerators based on superconducting rotor coils are considered for future large off-shore wind turbines for their low weight and compact design, and for their possibility to reduce costs. In the 10-20 K temperature range, MgB2 superconductors carry current densities 100 times higher than standard copper conductors at room temperature at one tenth of the wire cost per unit carried current. In the framework of the European project INNWIND.EU, an MgB2 superconducting generator pole will be designed, built and tested. Some of the design aspects of this work with emphasis on the winding process and associated coil insulation are discussed. An overall high current density in the coil is of crucial importance to obtain clear benefits compared to conventional solutions. The wire itself may be the most important parameter in that respect. However, the overall current density of the coil is also influenced by the thickness of the turn-to-turn electrical insulation. Here we discuss the impact of the insulation and suggest the use of a one-step winding process, employing wet-winding, where the applied epoxy also constitutes the insulation layer between turns. In this way the coil is densified by approximately 10% compared to the use of an additional, dedicated, electrical insulation like Kapton for wet-winding or glass-fibre for dry-winding followed by vacuum impregnation. We show the results of a trial winding of 500 m of MgB2 superconducting wire into a double pancake coil using the wet-winding technique. The coil is tested for contacts between the turns to evaluate the suggested one-step wet-winding process

Design optimization of ironless multi-stage axial-flux permanent magnet generators for offshore wind turbines

Direct-driven ironless-stator machines have been reported to have low requirements on the strength of the supporting structures. This feature is attractive for offshore wind turbines, where lightweight generators are preferred. However, to produce sufficient torque, ironless generators are normally designed with large diameters, which can be a challenge to the machine’s structural reliability. The ironless multi-stage axial-flux permanent magnet generator (MS-AFPMG) has the advantages of ironless machines but a relatively small diameter. The objective of this article is to present the design optimization and performance investigation of the ironless MS-AFPMG. An existing design strategy, which employs two- and three-dimensional static finite element analyses and genetic algorithm for machine optimization, is improved with the aim of reducing the calculation load and calculation time. This improved design strategy is used to investigate the optimal ironless MS-AFPMG. Some intrinsic features of this kind of machine are revealed

Toward a theory of repeat purchase drivers for consumer services

The marketing discipline’s knowledge about the drivers of service customers’ repeat purchase behavior is highly fragmented. This research attempts to overcome that fragmented state of knowledge by making major advances toward a theory of repeat purchase drivers for consumer services. Drawing on means–end theory, the authors develop a hierarchical classification scheme that organizes repeat purchase drivers into an integrative and comprehensive framework. They then identify drivers on the basis of 188 face-to-face laddering interviews in two countries (USA and Germany) and assess the drivers’ importance and interrelations through a national probability sample survey of 618 service customers. In addition to presenting an exhaustive and coherent set of hierarchical repeat-purchase drivers, the authors provide theoretical explanations for how and why drivers relate to one another and to repeat purchase behavior. This research also tests the boundary conditions of the proposed framework by accounting for different service types. In addition to its theoretical contribution, the framework provides companies with specific information about how to manage long-term customer relationships successfully

Connecting the dots between brand experience and brand loyalty: The mediating role of brand personality and brand relationships

This article critically examines consumer–brand relationships from the perspective of interpersonal relationship theory. Specifically, the authors investigate the relationship between brand experience and the two components of brand loyalty, namely purchase brand loyalty and attitudinal brand loyalty. The study also examines the link between brand experience and brand relationship variables, brand trust, brand attachment and brand commitment. In addition, the mediating role of brand personality and brand commitment in the relationship between brand experience and brandloyalty is investigated. Drawing on the results of an empirical cross-brand study from three product categories, the authors demonstrate that brand experience, brand personality and brand relationship variables (brand attachment and brand commitment) all affect the degree to which a consumer is loyal to a brand. On the basis of the findings, the authors offer guidelines to managers on how to build and sustain purchase and attitudinal brand loyalty by enhancing brand experience. The theoretical and managerial significance of the findings together with directions for future research are discussed

Apparatus for loss measurements under multidirectional and dc-bias flux in electrical steel laminations

Conventional standardized power loss measurements for electric steels are performed at flux densities with a single sinusoidal and unidirectional excitation. However, the flux inside electrical steel laminations can deviate significantly from the standard condition, and the loss is sensitive to such deviations of the flux in time and space. In this article, we describe the design and construction of an apparatus for loss measurements under two scenarios: (1) The main flux in the rolling direction is superimposed with flux in either the transverse or normal direction, while varying magnitude and phase angle between two fluxes and (2) the main flux having a dc-bias. The main flux in the rolling direction is generated in a square lamination frame by the current in excitation coils. The transverse and normal direction fluxes are generated by the current in auxiliary excitation coils wound around powder cores. The dc-bias flux is created either by an ac current with a small dc offset in the excitation coils or by a separate coil excited by a dc current. We implement and compare the two dc-bias methods and discuss the commons and differences. Finally, we present experimental results showing the possibilities for loss measurements under the combined action of magnetic flux in different directions and under dc-bias.acceptedVersio

Advanced Fault Detection of Synchronous Generators using Stray Magnetic Field

2022 IEEE. Personal use of this material is permitted. Permissíon from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertisíng or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works[EN] Many methods used for precise fault detec tion in salient pole synchronous generators (SPSGs) often require a priori knowledge of the healthy case, but this requirement impedes application of the methods since an accurate analysis of the different machine quantity wave forms is not usually carried out during commissioning. The inspection and maintenance processes in SPSGs are also costly and time-consuming; therefore, reliable methods that can detect and discriminate between different faults without comparison with the healthy condition are highly desirable. This paper proposes a precise method for de tection and discrimination between different fault types in SPSG. The method does not require healthy machine data and is applied to diagnose both inter-turn short circuits (ITSC) in the field winding and dynamic eccentricities (DE). The proposed non-intrusive detection algorithm is based on advanced signal analysis of stray magnetic field data and can be applied during SPSG operation. The method is highly precise for monitoring the condition of the rotor field winding and yields a unique pattern for diagnosing possible ITSC faults. Moreover, a distinctive pattern for the DE fault enables the discrimination between both consid ered failures, even if they are present at the same time. The proposed method is validated through finite element modeling and experimentally on a 100 kVA and a 22 MVA SPSG to demonstrate its applicability in real power plants.This work was supported by the Norwegian Research Centre for Hydropower Technology partly funded by the Research Council of Norway under Contract 257588.Ehya, H.; Nysveen, A.; Antonino-Daviu, JA. (2022). Advanced Fault Detection of Synchronous Generators using Stray Magnetic Field. IEEE Transactions on Industrial Electronics. 69(11):11675-11685. https://doi.org/10.1109/TIE.2021.31183631167511685691

Detailed magnetic field monitoring of short circuit defects of excitation winding in hydro-generator

The excitation windings of the synchronous generators are generally reliable. However, electrical, mechanical, and thermal stresses that the machine is exposed to during its operation leads to the inter-turn and ground insulation faults. On-line condition monitoring could provide a valuable real-time assessment of the synchronous generator. It could discriminate gradual aggravating defects at an incipient stage before it leads to irreversible and costly damages. On-line monitoring of the air gap magnetic field has been used in different types of electrical machines. However, some concerns should be considered when applying this method to the salient pole synchronous generators (SPSG), especially in the SPSG, with a large number of turns per poles that show less or lack of sensitivity to a fault. This difficulty could be solved by wise locating of the Hall effect sensor, choosing precise sampling rate, re-sampling the data and signal processing approach. In this paper, detailed online monitoring of the air gap magnetic field under the excitation winding defect is proposed. A procedure that could detect the severity and location of the fault-based on different analyzing methods of flux density in no-load and full load is proposed. The nominated approach is examined by using numerical modeling and a experimental test rig with a 100 kVA SPSG. It is proven that the air gap magnetic field spectrum could provide a reliable assessment of the machine under the short circuit fault of the rotor field winding

Detailed Magnetic Field Monitoring of Short Circuit Defects of Excitation Winding in Hydro-generator

The excitation windings of the synchronous generators are generally reliable. However, electrical, mechanical, and thermal stresses that the machine is exposed to during its operation leads to the inter-turn and ground insulation faults. On-line condition monitoring could provide a valuable real-time assessment of the synchronous generator. It could discriminate gradual aggravating defects at an incipient stage before it leads to irreversible and costly damages. On-line monitoring of the air gap magnetic field has been used in different types of electrical machines. However, some concerns should be considered when applying this method to the salient pole synchronous generators (SPSG), especially in the SPSG, with a large number of turns per poles that show less or lack of sensitivity to a fault. This difficulty could be solved by wise locating of the Hall effect sensor, choosing precise sampling rate, re-sampling the data and signal processing approach. In this paper, detailed online monitoring of the air gap magnetic field under the excitation winding defect is proposed. A procedure that could detect the severity and location of the fault-based on different analyzing methods of flux density in no-load and full load is proposed. The nominated approach is examined by using numerical modeling and a experimental test rig with a 100 kVA SPSG. It is proven that the air gap magnetic field spectrum could provide a reliable assessment of the machine under the short circuit fault of the rotor field winding