2,316 research outputs found

    Comparison of Superposition Equivalent Loading Methods for Induction Machine Temperature Tests

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    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

    Progressive collapse induced by fire and blast

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    Comprehensive finite element modelling of key elements is essential to improve the robustness assessment of structures subjected to a coupled effect of fire and blast. Focusing the attention on steel structures, a method for a realistic multi-hazard approach is presented. The problem has been investigated at the material level first and then at the structural level. The material level was studied performing a detailed experimental investigation in a wide range of strain rates and temperatures. A typical structural steel, namely S355, has been studied. A Split Hopkinson Tensile Bar equipped with a water-cooled induction heating system was used for the mechanical characterisation at high strain rates (300 1/s, 500 1/s and 850 1/s) and in a wide range of temperatures (20C, 200C, 400C, 550C, 700C and 900C). A Hydro-Pneumatic machine and a universal electromechanical testing machine were used for intermediate (5 1/s and 25 1/s) and quasi-static (0.001 1/s) strain rate tests at room temperature, respectively. Results showed that the S355 structural steel is strain rate sensitive, keeping its strain hardening capacity with increasing strain rates. The temperature effect was studied by means of the reduction factors for the main mechanical properties. Results at high strain rates highlighted also the blue brittleness phenomenon between 400C and 550C. The link between the material and the structural level is a material constitutive law able to take into account the strain rate sensitivity and the thermal softening. The widely used constitutive law proposed by Johnson and Cook was calibrated using the experimental results. A critical review of this material model highlighted a perceptible variation of the thermal softening parameter at different temperatures. Following a fitting approach, a modification of the dimensionless temperature (T*) has been proposed.The structural level was numerically investigated adopting the calibrated material model. Explicit non-linear dynamic analyses of a steel column under fire conditions and followed by an explosion were performed. The commercial code LS-DYNA was used. A method for a realistic multi-hazard approach has been proposed by studying the residual load bearing capacity. The results can be also of great interest to establish the initial conditions that could potentially lead to the onset of progressive collapse in steel framed structures under a combined effect of fire and blast. As expected, the results indicated that the load bearing capacity is influenced by the stand-off distance, the charge size as well as the column boundary conditions. The time of fire loading at which an explosion is triggered is a critical parameter as well

    Development of new methods for nonintrusive induction motor energy efficiency estimation

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    Induction motors (IMs) are the most widely used motors in industries. They constitute about 70% of the total motors used in industries and are the largest energy consumers in industrial applications. As a result of the increasing need for energy savings and demand-side management, the development of methods for accurate energy efficiency estimation has become a crucial area of research. While several methods have been proposed for induction motor efficiency determination, majority of the methods cannot be easily applied in the field owing to the intrusive nature of the test procedures involved. This PhD work presents some novel methods for nonintrusive efficiency estimation of induction motors operating on-site using limited motor terminal measurements and nameplate data. The first method is developed for induction motors operating on sinusoidal supply source (line-fed). The method uses a modified inverse Г-model equivalent circuit with series core loss arrangement to mitigate the inherent problems of higher computational burden and parameter redundancy associated with the conventional equivalent circuit method. Furthermore, a new method is presented for estimating the friction and windage loss using the airgap torque and motor nameplate data. The proposed Nonintrusive Field Efficiency Estimation (NFEE) technique was validated experimentally on four different induction motors for both balanced and unbalanced voltage supply conditions. The results demonstrate the accuracy of the proposed NFEE method and confirm its advantage over the conventional equivalent circuit method. In addition to the problem of unbalanced voltage supply, the presence of harmonics significantly affects the operation of induction motors. The second novel approach for estimating efficiency proposed in this PhD work extends the NFEE method to cover for non-sinusoidal supply condition. The method considers the variation of core loss, rotor bar resistance and leakage inductance due to time harmonics and skin effects. Finally, the efficiency estimations are compared to the IEC/TS 60034-2-3 in the case of a balanced non-sinusoidal supply condition. This allows not only the efficiency comparison but also the loss segregation analysis on the various components of the motor losses. In the case of an unbalanced supply, the efficiency results are compared to measured values obtained based on the direct input-output method. In both the first and second methods, a robust Chicken Swarm Optimization (CSO) algorithm has been used for the first time in conjunction with a simplified inverse Г-model EC to correctly determine the induction motor parameters and hence its losses and efficiency while inservice. As Variable Frequency Drives (VFDs) continue to dominate industrial process control, there is a need for stakeholders to quantify the converter-fed motor losses over a wide range of operating frequency and loading conditions. Although there is an increase in legislative activities, particularly in Europe, towards the classification and improvement of energy efficiency in electric drive systems, the handful of available standards for quantifying the harmonic losses are still undergoing validation. One of such standards is the IEC/TS 60034-2-3, which has been lauded as a step in the right direction. However, its limitation to rated motor frequency has been identified as one of its main weaknesses. Therefore, the third method proposed in this research demonstrates how the IEC/TS 60034-2-3 loss segregation methodology at nominal frequency can be extended over the constant-torque region of an induction motor (IM). The methodology has been validated by testing two motors using a 2-level voltage source inverter (VSI) in an open-loop V/F control mode. The results provide good feedback to the relevant IEC standards committee as well as guidance to stakeholders

    Cyclic creep behaviour of 99.85 percent pure copper

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    Dynamic stiffness and damping prediction on rubber material parts, FEA and experimental correlation

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    The final objective of the present work is the accurate prediction of the dynamic stiffness behaviour of complex rubber parts using finite element simulation tools. For this purpose, it becomes necessary to perform a complex rubber compound material characterisation and modelling work; this needs two important previous steps. These steps are detailed in the present document together with a theoretical review of viscoelastic visco-elasto-plastic models for elastomers. Firstly, a new characterisation method is proposed to determine the degree of cure of rubber parts. It is known that the degree of cure of rubbers bears heavily on their mechanical properties. This method consists of the correlation of swelling results to rheometer data achieving a good agreement. Secondly, the influence of the strain rate used in static characterisation tests is studied. In this step, a new characterisation method is proposed. The latter characterisation method will be used to fit extended hyperelastic models in Finite Element Analysis (FEA) software like ANSYS. The proposed method improves the correlation of experimental data to simulation results obtained by the use of standard methods. Finally, the overlay method proposed by Austrell concerning frequency dependence of the dynamic modulus and loss angle that is known to increase more with frequency for small amplitudes than for large amplitudes is developed. The original version of the overlay method yields no difference in frequency dependence with respect to different load amplitudes. However, if the element in the viscoelastic layer of the finite element model are given different stiffness and loss properties depending on the loading amplitude level, frequency dependence is shown to be more accurate compared to experiments. The commercial finite element program Ansys is used to model an industrial metal rubber part using two layers of elements. One layer is a hyper viscoelastic layer and the other layer uses an elasto-plastic model with a multi-linear kinematic hardening rule. The model, being intended for stationary cyclic loading, shows good agreement with measurements on the harmonically loaded industrial rubber part

    Non-intrusive efficiency estimation of inverter-fed induction machines

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    Motorised loads using induction machines use approximately 60% of the electricity globally. Most of these systems use three-phase induction motors due to their robustness and lower cost. They are often installed in continuously operating industrial plants/applications that require no operational interruptions. Whilst most of these induction machines are supplied from ideally sinusoidal supplies, applications are emerging where induction machines are fed from non-sinusoidal supplies. In particular, pulse width modulated inverters realize efficient control of induction machines in many automated industrial applications. From an energy management perspective, it is vital to continually assess the efficiency of induction machines in order to initiate replacement or economic repair. It is therefore of paramount importance that reliable and non-intrusive techniques for efficiency estimation of induction machines be investigated, that consider sinusoidal and non-sinusoidal supplies. This work proposes a non-intrusive efficiency estimation technique for inverter–fed induction motors that is based on harmonic regression analysis, harmonic equivalent circuit parameter estimation and harmonic loss analysis using limited measured data. Firstly, considerations for inverter-fed induction motor equivalent circuit modelling and parameter estimation techniques suitable for non-intrusive efficiency estimation are presented and the selection of one equivalent circuit for analysis is justified. Measured data is obtained from two different induction motors on a flexible 110kW test rig that utilises an HBM Gen 7i data acquisition system. By measuring voltage, current and input power at the supply terminals of the inverter-fed motor, the fundamental equivalent circuit parameters are estimated using population based incremental learning algorithm and compared with those obtained from the IEC 60034-2-1 Standard. The harmonic parameters are estimated using the bacterial foraging algorithm basing on the input impedance of the motor at each harmonic order. A finite harmonic loss analysis is carried out on the tested induction motors. The proposed techniques and harmonic loss analysis provide accurate efficiency estimates of within 1.5% error when compared to the direct method. Lastly, a related non-intrusive efficiency estimation technique is proposed that caters for a holistic loss contribution by all harmonics. The efficiency results from the proposed techniques are compared to those obtained from the IEC-TS 60034-2-3 Technical Specification and a direct method. The estimated efficiencies are comparable to those measured by the Technical Specification and a direct method within 2% error when tested on 37kW and 45kW PWM inverter-fed motors across the loading range. Furthermore, this work conducts a comprehensive non-intrusive rotor speed estimation comparative analysis in order to recommend the best technique(s), in terms of intrusiveness, accuracy and computational overhead. Errors of less than 1% have been reported in literature and experimental verification when using vibration analysis, Motor Current Signature Analysis (MCSA), Rotor Slot Harmonic (RSH) and Rotor Eccentricity Harmonic (REH) analysis techniques in inverter-fed IMs

    Study of stress relaxation and strain recovery in elastomeric compounds used in pipe seals

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    Elastomer compounds have been used in pipe seals for many decades, with their main problem, the stress relaxation due to various mechanisms. In these applications, a service life of more than fifty years is expected- and obtained. The purpose of the programme was to establish mathematical models to enable longevity of seals to be predicted from laboratory measurements. It seemed that stress relaxation in compression, together with strain recovery measurements, would provide a basis for such an investigation. Accordingly, such tests were carried out with up to 23 rubber compounds, at temperatures of 5°, 23°, 40°, 70°, 100° and and 125° C, with environments of air, mains water and town gas. The work outlined above is the main thrust of the programme, the data obtained being the raw material for the development and assessment of mathematical models associated with the viscoelasticity of the various rubbers. This work has been supported by supplementary investigations, including: effect of loading rate step changes in temperature inclusion (or not) of mechanical working of the specimen before testing use of solid phase lubricant changing the dimensions of the specimen comparison of air environment with water immersion, and town gas comparison of air environment with vacuum and nitrogen An important facet of the work has been the comparison of tensile behaviour with the bulk of the work carried out in uniaxial compression. A comparatively novel property has been introduced in this work: strain recovery after compression. This has proved to be a property related to 'permanent-set', yet more amenable to interpretation and correlation, recovery data are now available for most of the conditions in the stress relaxation programme whilst additional results have been obtained from compression set equipments. The other objective of this programme is to investigate short comings of BS 2494-1986, the current rubber seal specification, and to suggest new techniques such as strain recovery. Finally, the behaviour of seals in simulated service has been investigated to compare with the data generated in the main programme

    High Strain-Rate and Temperature Behaviour of Metals: Advanced Testing and Modelling

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    The purpose of the thesis was the prediction of the dynamic behaviour of metals. In order to investigate the mechanical response of metals in dynamic conditions, different experimental techniques were developed and used. The experimental data were analyzed through different procedures with the aim to provide consistent methodologies suited to extract sets of model parameters usable in the commercial FE codes

    Impact of voltage distortion on energy efficiency of induction machines and line start permanent magnet machines

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