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[en] This paper addresses a problem that occurs in many small appliances. As such, it is an important problem of energy utilization. To improve the performance of a single phase capacitor start/run induction motor, FET type power transistors could be used to replace a SCR H bridge. Such a configuration can lead to a simpler and more inexpensive circuit for the electronically controlled capacitor. In this paper, ICs and an OP-AMP are used to design an electronically controlled capacitor for a single phase induction motor. The design can compensate for the input voltage fluctuations that are present in the normal operation of the motor. In addition, an improvement in its performance can be obtained. At present, the use of a tachometer can be considered a disadvantage of the proposed scheme. Thus, a configuration that enables removal of the tachometer, while maintaining reasonable cost, is desirable. In addition, replacing the ac capacitor with one rated for dc can lead to a system reduction, in addition to a considerable reduction in the size of the circuit due to the use of integrated circuits
[en] Performance analysis of three phase induction motors under supply voltage unbalance conditions is normally conducted using the well-known symmetrical components analysis. In this analysis, the voltage unbalance level at the terminals of the machine is assessed by means of the NEMA or IEC definitions. Both definitions lead to a relatively large error in predicting the performance of a machine. A method has recently been proposed in which, in addition to the voltage unbalance factor (VUF), the phase angle has been taken into account in the analysis. This means that the voltage unbalance factor is regarded as a complex value. This paper shows that although the use of the complex VUF reduces the computational error considerably, it is still high. This is proven by evaluating the derating factor of a three phase induction motor. A method is introduced to determine the derating factor precisely using the complex unbalance factor for an induction motor operating under any unbalanced supply condition. A practical case for derating of a typical three phase squirrel cage induction motor supplied by an unbalanced voltage is studied in the paper
[en] Research highlights: → We have presented a novel approach to detect dynamic eccentricity in round rotor synchronous motors. → We have introduced an efficient index based on processing torque using time series data mining method. → The stator current spectrum of the motor under different levels of fault and load are computed. → Winding function method has been employed to model healthy and faulty synchronous motors. -- Abstract: In this paper, a novel approach is presented to detect dynamic eccentricity in round rotor synchronous motors. For this, an efficient index is introduced based on processing developed torque using time series data mining (TSDM) method. This index can be utilized to diagnose eccentricity fault and its degree. The capability of this index to predict dynamic eccentricity is illustrated by investigation of load variation impacts on the nominated index. Stator current spectrum of the faulty synchronous motor under different loads and dynamic eccentricity degrees are computed. Effects of the dynamic eccentricity and load variation simultaneously are scrutinized on the magnitude of 17th and 19th harmonic components as traditional indices for eccentricity fault diagnosis in synchronous motors. Necessity signals and parameters for processing and feature extraction are evaluated by winding function method which is employed to model healthy and faulty synchronous motors.
[en] Number of broken bars and varying load have been so far proposed in the literature in the process analysis of induction motors under broken rotor bars. In this paper, it is shown that there is the third factor which affects the diagnosis of the broken bars fault. This deterministic factor is the location of the broken bars which is determined precisely here. It is also shown that distribution of the broken bars over different poles of the motor reduces the amplitude of the harmonic components due to the fault. In this paper, the stator current frequency spectrum of a faulted induction motor is obtained for all cases in which four broken bars are distributed over poles of the motor. It is shown that the amplitudes of harmonics (1 ± 2s)fs are a suitable index for locating the rotor bars breakage. In this paper, the torque frequency spectrum of a faulted induction motor has been obtained for various cases of the bars breakage location and shown that the bars breakage location influences the amplitudes of harmonic components 2sfs in the torque frequency spectrum. Time stepping finite element method (TSFEM) is used to model an induction motors with rotor broken bars. In this modeling, geometrical and physical characteristics of all parts of the motor, spatial distribution of stator windings, slots on both sides of the air gap and non-linear characteristic of the core materials are included. Meanwhile the current of the broken bar is taken to be non-zero, instead resistance of the broken bar is considered large enough. In fact, this is the real case, because there is an inter-bar current within the broken bar induction motor. Since there is noise, unbalanced magnetic pull and arc in the broken bar induction motor, acceleration of the faulty motor up to the steady-state is considered here. It is indicated that the location of the rotor bars has significant effect upon the torque of the faulty motor and when the broken bars concentrate over one pole of the motor, the torque of faulty motor oscillates more
[en] Simultaneous static eccentricity and broken rotor bars faults, called mixed-fault, in a three-phase squirrel-cage induction motor is analyzed by time stepping finite element method using fast Fourier transform. Generally, there is an inherent static eccentricity (below 10%) in a broken rotor bar induction motor and therefore study of the mixed-fault case could be considered as a real case. Stator current frequency spectrum over low frequencies, medium frequencies and high frequencies are analyzed; static eccentricity diagnosis and its distinguishing from the rotor bars breakage in the mixed-fault case are described. The contribution of the static eccentricity and broken rotor bars faults are precisely determined. Influence of the broken bars location upon the amplitudes of the harmonics due to the mixed-fault is also investigated. It is shown that the amplitudes of harmonics due to broken bars placed on one pole are larger than the case in which the broken bars are distributed on different poles. In addition, influence of varying load on the amplitudes of the harmonics due to the mixed-fault is studied and indicated that the higher load increases the harmonics components amplitudes due to the broken bars while the static eccentricity degree decreases. Simulation results are confirmed by the experimental results.