2-D Magnetomechanical Transient Study of a Motor Suffering a Bar Breakage

© 1972-2012 IEEE. The analysis of the vibration response of electrical machines has importance in noise prediction and more recently, diagnosis of electrical faults, especially in the industrial environment, where it is a well-known technique. This work assesses the performance of a strongly coupled two-dimensional (2-D) magnetomechanical approach, as directly available in multiphysics software, for the simulation of an induction machine under heavy operational conditions: a direct-on-line startup. Both healthy and broken bar states are simulated in a time span long enough to allow the detailed study of the varying frequency components. The results yield, in addition to the usual electrical and magnetic quantities, electromagnetic-induced vibration components in the stator. A comparison with current and vibration experimental data is also performed showing a good agreement with variable frequency components and certain limitations concerning their amplitude

Study of thermal stresses developed during a fatigue test on an electrical motor rotor cage

© 2018 Structural defects in the rotor cage of large electrical machines significantly impact their expected operational lifetime. This work presents the results of simulating the thermal stresses developed in a rotor cage during a fatigue test in which a bar breakage was achieved. A combined model featuring electrical, thermal and mechanical stages as well as three different meshes reflecting a progressing narrowing of one of the bars in its junction to the end ring are used for this purpose. The experimentally implemented startup and plug stopping transients are reproduced as well as, for comparison, the stall operation. The resulting stress levels are in agreement with the progression of the damage and concur with the stator measurements. Based on the analysis of the simulated rotor magnitudes, a strategy to diminish the thermal stresses in a damaged cage is proposed

Analysis of an on-line superconducting cryofan motor for indirect cooling by LH2

This work relates to the study of an electrically powered cryofan for circulating close-loop cooling helium gas for superconducting applications with the following features: - Absence of any seal that can leak the pumped fluid or provide a path for heat transfer and require maintenance and/or is prone to failures. - The use of high temperature superconducting (HTS) stacks on the fan-rotor that, below critical temperature, can be magnetized contributing to the driving torque. The absence of electrically connected equipment as well as the lack of any seal, makes this arrangement especially suitable for reliable cryogenic helium gas circulation. Because HTS stacks cannot provide magnetic flux above Tc, during the initial stages of operation, in the presented study we analyse torque that will be provided by the passive iron components of the machine (reluctance torque, due to the saliency of the rotor) and by auxiliary permanent magnets or alternatively magnetizing coils

Computation of Superconducting Stacks Magnetization in an Electrical Machine

Superconducting technology offers the prospect of sharply increase the power density of rotating electrical machines, especially in the low speed, high torque range, with impact in applications such as wind energy and aircraft propulsion. Among the enabling technologies, stacks consisting of piling up layers of high temperature superconductor may provide a source of magnetic flux density for torque production, without the complexity of superconducting wound rotor poles. For this to happen, careful designs, optimizing electromagnetic, mechanical and thermal aspects at the same time, must be developed. In that sense, this work applies a recently developed combined electromagnetic formulation to compute the magnetization level of high temperature superconductor stacks installed in the airgap of an electrical motor after field cooling magnetization. The results are congruent with the applied field, show a strong interaction between teeth and stacks and provide a way of initializing the state of the machine prior to operation.Horizon 2020 research innovation programme under grant agreement No 7231119 (ASuMED consortium) and EPSRC grant EP/P000738/

Particle filter-based estimation of instantaneous frequency for the diagnosis of electrical asymmetries in induction machines

"© 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising 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.” Upon publication, authors are asked to include either a link to the abstract of the published article in IEEE Xplore®, or the article’s Digital Object Identifier (DOI).Fault diagnosis of induction machines operating under variable load conditions is still an unsolved matter. Under those regimes, the application of conventional diagnostic techniques is not suitable, since they are adapted to the analysis of stationary quantities. In this context, modern transient-based methodologies become very appropriate. This paper improves a technique, based on the application of Wigner Ville distribution as time frequency decomposition tool, using a particle filtering method as feature extraction procedure, to diagnose and quantify electrical asymmetries in induction machines, such as wound- rotor induction generators used in wind farms. The combination of both tools allows tracking several variable frequency harmon- ics simultaneously and computing their energy with high accu- racy, yielding magnitudes and values similar to those obtained by the application of the fast Fourier transform in stationary operation. The experimental results show the validity of the approach for rapid speed variations, independently of any speed sensor.Climente Alarcon, V.; Antonino Daviu, JA.; Haavisto, A.; Arkkio, A. (2014). Particle Filter-Based Estimation of Instantaneous Frequency for the Diagnosis of Electrical Asymmetries in Induction Machines. IEEE Transactions on Instrumentation and Measurement. 63(10):2454-2463. doi:10.1109/TIM.2014.231011324542463631

Heat extraction from HTS tape stacks applied in a superconducting motor in different cooling conditions

Abstract The heat is generated inside the stack of superconducting tapes mounted on the surface of the electrical machine rotor during its operation and magnetization. Cooling of such stack presents challenges because of the layered structure of both tape, and stack. Moreover, the tapes should be electrically isolated to minimize the AC losses, that assumes gluing them, rather than soldering. The calculations consider a conductive heat dissipation also through the rotor iron. Results show that: liquid nitrogen provides an effective cooling; the temperature of the stack shows complex distribution patterns with the gaseous coolant. Additional preventive measures were analyzed to keep the stack operational in vacuum conditions.</jats:p

Frequency-dependent demagnetisation rate of a shielded HTS tape stack

Abstract This work presents results of investigation of crossed-field demagnetization in 2G high temperature superconducting stacks at temperatures in the range of 77 - 20 K and in a variable frequency, corresponding to the particular rotor application. We propose a method to reduce the demagnetization rate for a given stack configuration necessary for the superconducting rotor operating at a cryogenic temperature. This technique involves 3-D wrapping the stack of tapes with perpendicular layers of similar superconducting properties. Previous ‘proof of concept’ studies documented some improvements in flux demagnetisation reduction for basic configuration. In the present study a more advanced approach based on magnetic flux shielding is adopted. The presented results provide an important contribution to development for design solutions that aim to increase the operational time before remagnetisation of the stacks would be required.</jats:p

Superconducting Magnetic Heterostructured Components for Electric Motor Applications

Trapped flux magnets made by stacking high temperature superconducting tape portray an easy assembly with already available materials, high mechanical resistance, provided by the substrate and improved thermal stability, which enhances the trapped flux compared to bulks. This allowed reaching the world record of 17.7 T. The presented analysis expands previous work with wide superconducting tapes showing further pos-sible improvements in this kind of devices in order to be used as source of magnetic flux in electrical motors, substituting permanent magnets. The aims are to increase the trapped magnetic flux during magnetization and decrease the leakage flux at the edges of the magnet during the operation of the machine. This is expected to be achieved by either introducing new materials in-between the individual tapes, such as ferromagnetic layers, or modifying the composition of the substrate. The results of simulations using the H-formulation as well as experimental measurements are presented.EPSRC grant EP/P000738/

Advanced Analysis of Motor Currents for the Diagnosis of the Rotor Condition in Electric Motors Operating in Mining Facilities

© 1972-2012 IEEE. Predictive maintenance of electric motors is a topic of increasing importance in many industrial applications. The mining industry is not an exception; many electric motors operating in mining facilities are critical machines, and their unexpected failures may imply significant losses and can be hazardous for the users. Due to these facts, an increasing research effort has been dedicated to investigate new techniques that are able to provide a reliable diagnostic of the motor condition. Over recent years, monitoring of electrical quantities (e.g., motor currents) has emerged as a very attractive option for determining the health of several motor parts (rotor, eccentricities, bearings) due to its very interesting advantages: possibility of remote motor monitoring, noninvasive nature, simple application, broad fault coverage, etc. The traditional methods based on the analysis of motor currents during a steady-state operation [motor current signature analysis (MCSA)] are being complemented when not replaced by more reliable approaches. This paper applies an innovative transient-based methodology to several case studies referred to large motors operating in mining facilities. The results prove how this modern methodology enables us to overcome some important drawbacks of the classical MCSA, such as its unsuitability under varying speed conditions, and may provide an earlier indication of rotor electrical asymmetries under such working conditions

Testing of Surface Mounted Superconducting Stacks as Trapped-Flux Magnets in a Synchronous Machine

Stacks of high temperature superconducting tapes may offer a technically affordable solution for the application of superconducting materials as trapped-flux magnets in the rotor of synchronous electrical machines. Nevertheless, several concerns must be first addressed, among others, the optimal procedure to induce the current vortexes previously to operation (magnetization), the survivability of these vortexes in the electromagnetic environment present in an electrical machine and the accuracy of recently developed numerical models. With the aim of exploring such practicalities, this paper presents a modified synchronous machine to test under liquid nitrogen conditions thin stacks of superconducting tapes. The machine is run under realistic conditions: currents in the stacks are induced from the stator, then the shaft is rotated and finally the machine is connected to a load, working as a generator. The results confirm previous numerical and experimental studies and establish a procedure for assessing the behavior of stacks in their actual operational environment.Also EPSRC EP/P000738/