Electromechatronic Systems Research Center

Covilhã, Portugal

Electromechatronic Systems Research Center

Covilhã, Portugal
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Gyftakis K.N.,Coventry University | Antonino-Daviu J.A.,Polytechnic University of Valencia | Garcia-Hernandez R.,Polytechnic University of Valencia | McCulloch M.D.,University of Oxford | And 3 more authors.
IEEE Transactions on Industry Applications | Year: 2016

It has been shown in the past that the zero-sequence current spectrum can be reliably used to detect broken bar faults in induction motors. Previous work was carried out with extensive FEM analysis. Although it allows detailed study of spatial and time-dependent electromagnetic characteristics of induction motors, FEM is a heavily time-consuming tool and this limits full study. So, in this work, extensive experimental testing has been performed to validate the zero sequence current spectrum for detecting rotor asymmetries. Three identical induction motors have been used: one healthy, one with a broken rotor bar, and one with two broken rotor bars. The motors were tested under different voltage supply levels and with different mechanical loads. The zero-sequence current spectrum was calculated after measuring the three phase currents. It is for the first time experimentally shown that this approach offers greater diagnostic potential than traditional MCSA. © 2016 IEEE.


Oliveira L.M.R.,University of Algarve | Oliveira L.M.R.,Electromechatronic Systems Research Center | Cardoso A.J.M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,University of Beira Interior
IEEE Transactions on Power Delivery | Year: 2015

This paper presents a general approach to compute the leakage inductances of power transformers with turn-to-turn winding faults. The leakage inductances are obtained by using well-known conventional formulas, adapted to the asymmetrical conditions produced by the interturn fault in the leakage flux distribution. Two methods for calculating the leakage inductances are presented: the first requires detailed information about the geometry of the windings whereas the second uses simplifying assumptions, allowing to express the leakage inductances as a function of the nameplate short-circuit inductance, the number of turns, and core dimensions. A leakage inductance model of the transformer with faulty turns is also proposed, which is based on the three-winding transformer theory. This leakage inductance equivalent circuit can be easily integrated into other electromagnetic transient simulators. The results obtained from the application of the analytical methods and the equivalent circuit are validated using data obtained from finite-element analysis and experimental short-circuit tests. © 1986-2012 IEEE.


Ferreira A.P.,Polytechnic Institute of Bragança | Ferreira A.P.,Electromechatronic Systems Research Center | Leite A.V.,Polytechnic Institute of Bragança | Leite A.V.,Electromechatronic Systems Research Center | Costa A.F.,FEUP
Proceedings - SDEMPED 2015: IEEE 10th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives | Year: 2015

Evaluation and minimization of cogging torque in Axial Flux Permanent Magnet (AFPM) machines become essential specially in direct drives for low speed applications. This paper presents a comprehensive analysis of the cogging torque in AFPM machines designed for low speed applications and mitigation methods are proposed. Evaluation methodologies of the cogging torque based on Finite Element Analysis (FEA) computations are discussed and applied to a double-sided, internal rotor, AFPM reference machine. From the performance comparison of Maxwell stress tensor and virtual work methods on the evaluation of cogging torque, it is possible to conclude that the latter overestimates the amplitude of the cogging torque into a considerable extent. © 2015 IEEE.


Gyftakis K.N.,University of Oxford | Drif M.,University of Science and Technology of Oran | Drif M.,University of Beira Interior | Cardoso A.J.M.,University of Beira Interior | Cardoso A.J.M.,Electromechatronic Systems Research Center
Proceedings - SDEMPED 2015: IEEE 10th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives | Year: 2015

It has been noted in previous works that, when there is a stator inter-turn fault, the third current harmonic increases in the line current frequency spectrum offering diagnostic potential. This phenomenon has been given many explanations in the past. Many causes have been reported that may produce and influence the third current harmonic, such as saturation, manufacturing imbalances, supply asymmetries, etc. This paper constitutes an effort to analyze and evaluate previous knowledge regarding the third line current harmonic in induction motors suffering from a stator inter-turn fault. The work is carried out with Finite Element Analysis (FEM). In this investigation, FEM is a valuable tool, because it allows the investigation of each parameter's influence on the third current harmonic, independently from the others. © 2015 IEEE.


Oliveira L.M.R.,University of Algarve | Oliveira L.M.R.,Electromechatronic Systems Research Center | Cardoso A.J.M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,University of Beira Interior
Proceedings - SDEMPED 2015: IEEE 10th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives | Year: 2015

This paper presents a comparison of two of the most sensitive methods to detect low-level turn-to-turn faults in the windings of three-phase transformers. The performance of the negative sequence component and of the space vector protection algorithms is tested under several internal and/or external fault conditions. The simulation results indicate that the fault detection sensitivity of both methods is very similar. © 2015 IEEE.


Yahia K.,University Mohamed Khider of Biskra | Yahia K.,University of Beira Interior | Sahraoui M.,University of Beira Interior | Sahraoui M.,University Mohamed Khider of Biskra | And 3 more authors.
Proceedings - SDEMPED 2015: IEEE 10th International Symposium on Diagnostics for Electrical Machines, Power Electronics and Drives | Year: 2015

Induction motors airgap-eccentricity fault detection has attracted the interest of many researchers in last decades. The Discrete Fourier Transform (DFT) has been widely used for that purpose. However, DFT can only give meaningful information for stationary signals. In this paper, an efficient time-domain technique based on a modified Prony's method for the airgap-eccentricity fault detection in induction motors is presented in order to overcome the DFT problems. Using this technique, the apparent power, as processed signal, is divided into short overlapped time windows, and each one is analyzed by the Least Squares Prony's method. The proposed technique allows tracking the frequencies and amplitudes of the airgap-eccentricity fault characteristic frequency component fr with a very high accuracy. A fault severity factor (FSF) based on fr amplitudes is defined. Simulation as well as experimental results are provided to illustrate the effectiveness and accuracy of the proposed method. © 2015 IEEE.


Stabile A.,Studio Energie Rinnovabili | Estima J.O.,Electromechatronic Systems Research Center | Estima J.O.,University of Beira Interior | Boccaletti C.,Electromechatronic Systems Research Center | And 3 more authors.
IEEE Transactions on Industrial Electronics | Year: 2015

Power converters are complex devices subject to failures that can lead to undesired stops. For this reason, many fault-tolerant topologies and strategies have been deeply studied, mainly focusing on improving the electromechanical behavior of the reconfigured drive after the fault. However, it is also very important to evaluate the possible increase of power losses. In this paper, a power loss analysis is performed on a current-controlled three-phase inverter supplying a permanent-magnet synchronous motor (just chosen as an example), for all the operating modes, starting from the fault occurrence until the faulty operation mode is established. This is particularly important because the effectiveness of a fault-tolerant control strategy depends on the possibility to maintain a continuous operation. The latter is ensured only if there is no such increment of the losses that the survival of the component is at risk. The simulations are validated by means of experimental tests, and the results are discussed. The method can be easily applied to other topologies and reconfiguration strategies. © 2014 IEEE.


Leite V.,Polytechnic Institute of Bragança | Leite V.,Electromechatronic Systems Research Center | Couto J.,Polytechnic Institute of Bragança | Ferreira A.,Polytechnic Institute of Bragança | And 2 more authors.
2016 IEEE International Energy Conference, ENERGYCON 2016 | Year: 2016

Pico-hydro power generation has a considerable untapped potential, able to contribute to the increased energy demand whilst ensuring a low environmental impact. The integration of these systems into microgrids is an emerging solution for the electrification of remote regions and also for self-sustainable power systems. The integration of cheap and wide spread technologies to interface small capacity hydro power systems with the grid has become essential in order to enable the exploitation of small rivers and shallows reservoirs resources among many other applications such as in water supply systems. This paper presents a design procedure to integrate pico-hydro generators into the grid using conventional and widespread photovoltaic inverters. © 2016 IEEE.


Sahraoui M.,University Mohamed Khider of Biskra | Sahraoui M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,University of Beira Interior | And 3 more authors.
IEEE Transactions on Industry Applications | Year: 2016

It is well known that rotor speed estimation assumes a paramount importance for the correct diagnosis of bearings, air-gap eccentricities, or rotor bar defects. In this paper, a new technique for rotor speed estimation using a modified Prony's method is proposed. The algorithm developed for this purpose is based on tracking the frequencies of the rotor slot harmonics (RSH) that exist in stator currents of most squirrel-cage induction motors. High-order RSH frequencies are used to avoid the possible effect of harmonics stemming from other sources. The proposed modified Prony's method shows a great ability for tracking RSH frequencies and then the rotation speed. In addition, this technique can deal with noisy and nonstationary signals and it requires only few data samples, which reduce considerably the computational time and data storage requirements. Consequently, the proposed algorithm is suitable for online implementation. The method's effectiveness is verified by simulation and experimental tests. © 2016 IEEE.


Sahraoui M.,University Mohamed Khider of Biskra | Sahraoui M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,Electromechatronic Systems Research Center | Cardoso A.J.M.,University of Beira Interior | Ghoggal A.,University Mohamed Khider of Biskra
IEEE Transactions on Industry Applications | Year: 2015

The knowledge of the broken rotor bar characteristic frequencies and amplitudes has a great importance for all related diagnostic methods. The monitoring of motor faults requires a high resolution spectrum to separate different frequency components. The discrete Fourier transform (DFT) has been widely used to achieve these requirements. However, DFT can give meaningful information only for stationary harmonics which cannot be guaranteed in real cases. In addition, a long data sequence is necessary for DFT to get high frequency resolution. Nevertheless, the signals are time varying, and the steady-state conditions can be lost for a long time acquisition. As a solution for these problems, this paper proposes an efficient time-domain technique based on a modified Prony method for the estimation of the frequencies/amplitudes of broken rotor bar faults. Using this technique, the stator current is divided into short overlapped time windows, and each one is analyzed by the least squares Prony method. The proposed technique provides a linear time-frequency/amplitude representation with high frequency resolution and adjustable time resolution. It is shown that this technique allows tracking the frequencies and amplitudes of the sidebands around the fundamental frequency component with a very high accuracy. The efficiency of the proposed method is verified by simulation and experimental tests. © 2014 IEEE.

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