Comparison of Superposition Equivalent Loading Methods for Induction Machine Temperature Tests

The superposition equivalent loading method proposed by international standards for testing induction machines allows to conduct temperature tests at reduced different conditions than rated and extrapolate the results to rated values. Much as this test is suitable for large machines that test facilities lack capacity to test, the principle is also applicable to small machines. However, its applicability to small machines has not been extensively studied yet. Furthermore, the three types of the method categorized in the standard IEEE 112-2017 have not been compared to establish their equivalence or otherwise. This paper reports an extensive test campaign on different small size induction motors to determine both the applicability of the method to small machines and to compare the equivalence of the three types of approach. Multiple reduced voltage and reduced current selections have also been investigated to assess the accuracy of the methods for different test conditions. Test results show that all the three alternative loading methods proposed by the standard seems to be practically equivalent, whit a goodness of fit of the obtained results that tends to improve as the machine rating increases

Enhanced Stray-Load Loss Measurements Through a Zig-Zag Variable Load Test Approach

This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consistsofalternativelyapplyingloadlevelshigherandlowerthan the rated load, so that the stator winding temperature zigzags aroundtheratedvalue.Hence,multiplereadingscanbeperformed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizesandpolecounts,applyingboththestandardvariableloadtest procedure and the proposed approach. The experimental results show that theproposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure

Simplified Thermal Model of Disk-Shaped Automotive Smart Braking Actuators

This paper articulates the challenges in the thermal modelling of surface-mounted permanent magnet motors for automotive brake-by-wire systems, which operate by injecting high dc currents in two of the three phases for short time intervals. This unconventional operation requires dedicated thermal models for the prediction of uneven heat distributions inside the machine. This study extends a previous work conducted on slender-shaped motors to a disk-shaped machine where the edge effects could compromise the model accuracy. Additionally, here efforts have been made to minimize the number of experimental tests needed for the correct calibration of the proposed phase-split lumped-parameters thermal models

Electrical Machine Topologies: Hottest Topics in the Electrical Machine Research Community

In this article, the state of the art in electrical machine design is outlined underlining the problems and challenges to be solved by engineers. As highlighted in this article, even if electrical machine design is often considered a mature issue from the technical and technological point of view, every year, new progresses and steps forward are made. New and more sophisticated design tools can be used worldwide, and innovative manufacturing processes, new insulation materials, and higher performance magnetic materials are available on the market. In addition, the evolution of the hardware used in digital control and new powerful power electronic devices represents a constant stimulus to improve the performance of electrical machines and reintroduce electrical machine structures that were not adopted in the past due to technological and technical constraints. As shown in this article, electrical machine design is an evergreen topic, and its importance is rising more each year under the push of more energy-saving requirements and higher-efficiency systems for electromechanical conversion. A green world will not be possible without electrical machines

Review of magnetic gear technologies and their applications in marine energy

The marine energy industry is in its early stages but has a large potential for growth. One of the most significant challenges is the reduction of operation and maintenance costs. Magnetic gears (MGs) offer the potential for long periods between maintenance intervals due to their frictionless torque transmission which could reduce these costs. This study presents a summary of the state of the art in MG technology and then investigates its potential for marine energy applications. A brief overview is given of the state of the marine energy industry and the environment in which marine energy converters (MECs) operate. A short history of MG development over the past century is then presented followed by a discussion of the leading MG technologies and their relative advantages. In order to demonstrate the potential of MGs in marine applications, the current technologies, i.e. mechanically geared and direct drive machines, are examined in terms of sizing, reliability and economic value using previous studies on a similar technology, namely wind. MGs are applied to four types of MECs to demonstrate how the technology can be incorporated. The potential to deploy at scale and potential obstacles to this are then discussed

Piston-driven numerical wave tank based on WENO solver of well-balanced shallow water equations

A numerical wave tank equipped with a piston type wave-maker is presented for long-duration simulations of long waves in shallow water. Both wave maker and tank are modelled using the nonlinear shallow water equations, with motions of the numerical piston paddle accomplished via a linear mapping technique. Three approaches are used to increase computational efficiency and accuracy. First, the model satisfies the exact conservation property (C-property), a stepping stone towards properly balancing each term in the governing equation. Second, a high-order weighted essentially non-oscillatory (WENO) method is used to reduce accumulation of truncation error. Third, a cut-off algorithm is implemented to handle contaminated digits arising from round-off error. If not treated, such errors could prevent a numerical scheme from satisfying the exact C-property in long-duration simulations. Extensive numerical tests are performed to examine the well-balanced property, high order accuracy, and shock-capturing ability of the present scheme. Correct implementation of the wave paddle generator is verified by comparing numerical predictions against analytical solutions of sinusoidal, solitary, and cnoidal waves. In all cases, the model gives satisfactory results for small-amplitude, low frequency waves. Error analysis is used to investigate model limitations and derive a user criterion for long wave generation by the model

A direct-drive wave energy converter with contactless force transmission system

Commonly proposed ocean wave energy converters (OWEC) use inefficient and maintenance demanding intermediate hydraulic and pneumatic systems. We propose a novel rotary direct-drive OWEC that eliminates these intermediate stages. The new device employs a contactless force transmission system (CFTS) comprising a “piston” and a “cylinder” and a ball screw to spin a conventional rotary generator. We present an analytical model of the OWEC and also propose a numerical technique that performs a coupled fluid-structure interaction simulation of the wave energy device in a 3-D numerical wave flume using a computational fluids dynamics (CFD) code. In previous investigations, the motion of floating bodies was prescribed rather than determined. The current method represents a significant advancement in that it determines the motion of the buoy from the dynamic solution of the fluid flow problem and the dynamic buoy motion problem. The technique was extended to assess the performance of two neighboring buoys and their interference effects.Keywords: direct-drive, ocean wave energy, fluid-structure interactio