Stator Phase Windings Research Articles

Diagnostics of inter-turn short circuits in phase stator windings of permanent magnet synchronous machines

BACKGROUND: Currently, electric buses are becoming more widespread in the segment of urban passenger transportation due to the absence of harmful emissions and low noise levels. Permanent magnet synchronous machines (PMSM) are widely used as a traction motor.
 One of the most promising methods of monitoring the technical condition of traction motors is diagnostics using monitoring tools installed on board of a vehicle. The advantages of such methods include the possibility of regular frequent condition checks (as opposed to much rarer diagnostics in stationary maintenance points) and a more rapid response to the development of identified malfunctions, which significantly reduces the cost of maintenance and repair of expensive equipment. The disadvantages include limitations associated with a shortage of layout space for the placement of diagnostic equipment, with the limited capabilities of on-board computer facilities for the transmission and storage of diagnostic information and with the complexity of computational procedures of built-in expert diagnostic systems.
 Concerning the types of operational failures of PMSMs, which are the most common and the most severe in terms of the cost of restoring operability, these are inter-turn short circuits in the stator windings, increased eccentricity of the air gap between the stator and the rotor, bearing damage, as well as damage of the mechanical gearbox coupled with the electric motor.
 AIM: Identification the diagnostic signs of inter-turn short circuits in the phase windings of a permanent magnet synchronous machine, helping to detect these malfunctions on board of route urban vehicles at an early stage.
 METHODS: A mathematical model of a permanent magnet synchronous machine with short-circuited turns of the phase winding, which makes it possible to study the behavior of the motor with a various number of short-circuited turns, has been developed.
 RESULTS: For the first time, the requirements for diagnostic features for the on-board diagnostic system of an urban electric bus, making it possible to detect inter-turn short circuits in the phase windings of traction electric motors at the early stages of the origin of a malfunction, are formulated.
 The main parameters of the process of digital registration of phase currents have been obtained, helping to do measurements and to transmit signals through the onboard information network of the electric bus.
 Using simulation modeling methods, it was found that the peak values of the linear spectrum of the total current vector are stable diagnostic signs that make it possible to detect inter-turn short circuits in the phase windings of traction motors at the early stages of the origin of the malfunction.
 CONCLUSION: The practical value of the study lies in the opportunity of using the proposed methods for diagnosing the technical condition of traction electric drive units in urban passenger electric transport.

Asynchronous generator replacement scheme with internal capacitive reactive power compensation

The relevance of using compensated induction machines in the generator mode of autonomous power supply systems is determined by their ability to provide a stable and reliable power supply even in the absence of an external grid. The research aims to develop a procedure for determining the characteristics of an equivalent circuit of compensated induction generators that considers the mutual influence between the main and additional phase windings of the armature. The theory of an idealised induction machine with the representation of electromechanical energy conversion processes and basic physical parameters in the form of equations of electrical equilibrium and drive motion was used to obtain the calculated characteristics of the generator’s operating modes of this class. The generalised system of differential equations made it possible to calculate dynamic and static processes for symmetrical and asymmetrical modes at given machine parameters under different methods of excitation and voltage stabilisation under variable load. For the practical implementation of modelling the parameters of an induction generator, the equations of electrical equilibrium of the stator and rotor circuits for the symmetrical steady-state mode are used, which is a special case of the generalised mathematical model of the machine for both transient and steady-state processes with constant parameters of the substitution scheme. Consideration of the structural and functional features of compensated induction generators was made possible by using a mathematical model with the armature winding divided into two coaxial or spatially offset half-windings. In this case, the number of calculation equations doubles. The use of an autotransformer scheme for switching on the stator phase half-windings to capacitors required the introduction of an additional differential equation for the electrical equilibrium of the stator phases. This made it possible to substantiate the values of active and inductive resistances used in the replacement circuit of an induction generator with internal capacitive reactive power compensation. The mutual inductive coupling of the main and additional half-windings of the generator stator phase windings due to both the operating magnetic flux and the magnetic fluxes of dissipation was considered. The practical significance of the obtained results is to increase the efficiency and stability of the power supply, which helps to reduce losses and improve the operation of electric power systems

ON THE REPRESENTATIVE SPACE PHASOR CONCEPT FROM THE DYNAMIC MODEL OF THE THREE-PHASE INDUCTION MACHINE

In the paper, based on the linear dynamic behavior models of the electrical and magnetic subsystems of the induction machine with three-phase symmetrical stator winding and polyphase rotor winding (cage type) in short circuit, the values ​​are represented, in the complex plane confused with the cross-sectional plane of the machine and the instantaneous polar angular positions of the amplitudes of the progressive (spinning) plane waves of the instantaneous resultant solenations of the machine windings, and correspondingly, the spatial phasors representative of the instantaneous electrical circuit scalar quantities of the stator phase windings and rotor equivalents of the machine are defined. The metric (length and orientation) of these representative spatial phasors allows their physical significance to be revealed.

Prony Method Estimation as a New Approach for Surge Comparison Testing in Turn Insulation Diagnostics for Three Phase Stator Windings

This article presents an evaluation of Prony method estimation and its implementation considerations for surge comparison test application in turn insulation diagnostics for three-phase stator windings. Surge testing diagnostics compares recorded surge voltage signals of motor winding, and a diagnostic is then defined with a defined value of EAR (error area ratio), which evaluates the difference between signals to determine a turn insulation diagnostic. First, an overview of surge testing is presented. Next, the Prony method and the considerations for its implementation in surge testing are described. Then, a numerical simulation is used to define a simulated turn fault surge voltage signal, where its parameters can be obtained with Prony method estimation and compared with EAR to evaluate its performance. Lastly, recorded surge test signals from two tested motors are used to validate Prony method estimation application for surge test diagnostics, where twelve recorded surge signals for no-fault and fault conditions were analyzed. The summary results of the surge signals parameter estimation are presented in the results and discussion section.

Excitation field and parameters of traction superconducting synchronous motor of pipeline transport

Movement of passenger crews in a rarefied air tube at speeds over 600 km/h involves the effect of magnetic levitation and a traction linear superconducting synchronous motor with a stator winding distributed along the length of the tube and a superconducting excitation system on the crew. Conditions of magnetic levitation stipulate that the position of the crew in the tube is characterized by six degrees of freedom, so a traction linear superconducting synchronous motor must be considered as a multi-stage dynamic system. However, in the “normal” operational mode, the problem is reduced to consideration of the system with one degree of freedom with the coordinate that determines the position of an inductor with superconducting winding and without ferromagnetic cores relative to the running magnetic field of the stator winding. The specifics of magnetic levitation of the moving crew, which consists in the possibility of its spatial displacement, cause the appearance of geometric parameters characterizing progressive and rotational perturbations of the coordinates of the center of inertia of the crew in expressions for mutual inductances between the superconducting excitation system, electromagnetic shield, and the stator phase windings.

Simulation of transients in an autonomous power system considering the generator and transformer magnetic core saturation

The paper considers transients in an autonomous power system consisting of a generator, a transformer, and a general load. The numerical method for simulating transients includes the possibility of the asymmetry of stator windings and magnetic core saturation of a generator and a transformer. The asymmetry is usually observed under synchronous machine faults such as turn-to-turn short circuits in the stator winding. The method is based on the solution of differential equations for the equilibrium of electromotive force and voltage drops in windings in phase coordinates in combination with the rotor rotation equation. In this case, a circuit of each phase stator winding is described by an equation that considers the difference in phase parameters. The mathematical model is developed in MATLAB. The model includes an unequal number of turns in phase windings that allows simulating the turn-to-turn short circuits without considering the occurrence of additional short-circuited circuits. The analysis of simulation results was performed under no-load operating conditions and in the presence of load. The obtained results demonstrated the influence of the saturation of magnetic systems on the parameters of normal and abnormal operating conditions in the power system.

Study of the Operating State of a Synchronous Motor Electric Drive by Means of Changes Estimation of the Stator Current Behavior

The article proposes a model for the research of the changes in the operating state of a three-phase synchronous motor used in an electric drive of the technological mechanisms. The model has been implemented in the MATLAB software environment based on the Park-Gorev equations, which has found wide application in Electromechanics. It has become possible to estimate during transient changes in the electromagnetic torque of the electric motor along the axes d and q, and stator currents in phases a, b, c, as well as the changes in the ratios of the currents of the reverse and direct sequence. It is confirmed that when the supply voltage of the network and the load torque of the technological mechanism change, in the stator phase windings, currents of the reverse sequence appear. For the considered electric drive motor, the reverse sequence current does not exceed 1.5% of the direct sequence currents, meanwhile the permissible limit according to the standard is 8%. The research model of the operating state of the synchronous motor can be successfully used to identify the pre-emergency state of the operated electric drive systems, assess the causes of their occurrence, and make optimal decisions. The obtained results can also be successfully used for intelligent diagnostics in order to develop automated control systems.

Performance Analysis of the Slip Power Recovery Induction Motor Drive System Under Unbalance Supply Voltages

This paper develops a mathematical model for analyzing the steady-state performance of the Slip Power Recovery Induction Motor Drive System (SPRIMDS) which operates under unbalance supply voltage conditions. The IEC definition indices of Voltage Unbalance Factor (VUF) and Complex Voltage Unbalance Factor (CVUF) which consist of magnitude and phase angle of the unbalance supply are used for the analysis. Also, this paper evaluates the impact of voltage unbalance and firing angle of the inverter on the stator and rotor motor parameters, motor currents, copper losses, efficiency, power factor, torque-speed characteristics, prediction of peak currents of the stator and rotor phase windings, and Total Harmonic Distortion (THD) of stator and rotor currents. The proposed mathematical model of SPRIMDS is validated using MATLAB-Simulink. The results have shown that the performance of the SPRIMDS and variation of motor currents, efficiency, THD and torque are depending on the magnitude of the voltage unbalance and inverter's firing angle.

Efficient index for detecting the stator winding interturn fault in six-phase squirrel-cage induction motors

Multi-phase electrical machines have recently drawn growing attention, among which; six-phase squirrel-cage induction motors (6PIMs) have gained a considerable share. 6PIMs are main candidates to be utilized in hybrid vehicles, electrical trains, ships, submarines, etc. Incipient fault diagnosis is an essential technology, which enables preventing serious damages to the machines and catastrophic interruption of them. The stator winding interturn fault is among the main incipient faults. Although, numerous studies have dealt with this fault in three-phase induction motors, there is a few studies concerning the 6PIMs. In this paper, the winding function approach is utilized to model, simulate and analyse the performance of the 6PIM with interturn fault in a stator phase winding. After examining the simulation results, an analytical method is followed to extract efficient graphic and quantitative indices for detecting the stator interturn fault and for evaluating its severity. The indices require sampling the stator phase currents only in one fundamental period, enable identifying the faulty stator phase, show good sensitivity to the fault severity and are almost insensitive to the load torque change. The stator voltage unbalance cannot mislead the fault detection method based on the indices. Various simulation and corresponding experimental test results confirm these merits.

Analysis of a Novel Three-phase Asynchronous Generator Based on Graph Theory for Supplying Single-Phase Load

This paper presents a novel three-phase star-connected stand-alone asynchronous generator (SAG) with only two capacitors, connected in series with two stator phase windings, for supplying power to single-phase resistive load. This new scheme has excellent voltage regulation (less than 1.7%) due to the presence of these two series capacitors and does not require any separate voltage regulating device making it very simple and cheaper. The symmetrical component theory has been used to form a simplified equivalent circuit of the scheme. Graph theory has been applied to the equivalent circuit to simplify the process of obtaining two non-linear higher-order equations which are solved using the binary search algorithm (BSA) to obtain the values of per unit frequency and magnetizing reactance. Accordingly, using the magnetization characteristics of the machine and the performance equations, the steady-state performance of the SAG has been obtained. To investigate the behavior of the SAG under transient conditions, such as voltage build-up, load switching and load perturbation, a dynamic model of the generator scheme has been developed on the basis of d-q axes theory in stationary reference frame including the effect of main and cross flux saturation. The simulated results have been validated through experimentation using an induction machine rated as 2 hp, 4-pole, 415 V, 3.5 A, 3-phase, 1440 rpm, 50 Hz. The simulated results closely agree with the experimental results, indicating the efficacy of the proposed approach. This can be a promising single-phase power generation scheme for supplying power in remote rural areas.

Extra Freedom Degrees of Six-Phase Induction Motors Used to Diagnose Stator Inter-Turn Faults

— Multi-phase electrical machines have recently drawn growing attention and usage, among which, 6-phase induction motors (6PIMs) have gained an important part. They are main candidates to be utilized in the oil and gas industries, hot rolling mill drives, pumps, ship propulsion, and traction. Condition monitoring and fault diagnosis are essential technologies, which enable incipient fault detection and removal in order to prevent serious damages to the machines and catastrophic interrupt of them. Among the incipient faults, the stator winding inter-turn fault is a rather frequent one. In recent decades, numerous studies have dealt with this fault in three-phase induction motors, however, a few reports are available concerning 6PIMs. This paper applies the winding function method to model and simulate the 6PIM with inter-turn fault in a stator phase winding. Then, using the extra degrees of freedom in 6PIM, an analytical method is used to define an efficient index for detecting the stator inter-turn faults. This index also identifies the faulty phase of the stator, shows good sensitivity to the fault severity and is almost insensitive to the load torque change. Various simulation studies and corresponding experimental test results confirm effectiveness of the proposed index.

Calculation of Inductive Resistances of Asynchronous Motor Windings at Rotor Eccentricity

In this paper, we propose a method for calculating the inductive resistances of asynchronous motor windings at rotor eccentricity. The eccentricity results from the displacement of the rotor axis relative to the axis of the stator bore and is accompanied by an uneven air gap. It does not lead to an immediate failure of the asynchronous motor, but is accompanied by a change in almost all electromechanical characteristics and increased energy consumption. In addition, the tension between the stator and the rotor increases and leads to an increase in the air gap unevenness and the subsequent rotor touching of the stator, i.e., the motor output out of service. Consequently, the detection of the rotor eccentricity at the early occurrence stages is an important problem. This requires a mathematical model of a three-phase asynchronous motor with the rotor eccentricity. For such a model, it is necessary to determine the inductive resistances of all motor windings. We propose magnetic flux schemes through the stator phase windings and the short-circuited inductor rotor winding to calculate the inductive resistances. We also propose to determine the inductive resistances using the zero and first members of the series of the average specific conductivity of the air gap obtained by expanding it in the Fourier series.

CHARACTERISTICS OF A CYLINDRICAL INDUCTOR OF A ROTATING MAGNETIC FIELD FOR TECHNOLOGICAL PURPOSES WHEN IT IS POWERED FROM THE MAINS AT A GIVEN VOLTAGE

Introduction. A computational analysis of the characteristics of an inductor of a rotating magnetic field for technological purposes is presented. The design of its stator is borrowed from a three-phase induction motor. The cylindrical cavity inside the stator is occupied by a working chamber into which a granular or liquid processed substance is loaded. The processing is carried out with elongated ferromagnetic elements moving with a magnetic field. Problem. The purpose of the article is a study of the electromagnetic, phase, and energy characteristics of an inductor at its operation under load mode with a given voltage of the stator winding. Methodology. The study is performed on the basis of numerical calculations of the magnetic field, taking into account the anisotropy of the low-magnetic medium in the working chamber. Its discrete medium is represented homogeneous with different magnetic permeabilities on mutually perpendicular axes. The technique of transition from the results of the magnetic field calculation to the electric, magnetic, phase and energy parameters of the inductor is given. This is facilitated by the electrical equivalent circuit of the stator phase winding, the equilibrium equation of its electrical quantities, vector diagrams and an iterative method for determining the current at a given voltage. Results. Mutual dependencies of a number of inductor parameters are formed into a family of characteristics exhibiting its properties in an operating mode with a changing load. Characteristics include such quantities as magnetic flux linkage of the stator winding, its current and EMF, phase shifts between them, electromagnetic torque, expended and useful power and its losses, power factor and efficiency. In this article, a feature of this mode is the stability of the stator winding voltage in the inductor. This complements the earlier studies of the inductor in the mode with stabilization of the winding current, which allows to compare these options. On the example of a test sample of an inductor, a number of its characteristics are shown, vector diagrams of its electric and magnetic quantities illustrating their mutual phase shifts are given. Practical value. The presented technique for determining the electric and magnetic quantities of the inductor and their phase relationships, and also the shown family of characteristics can contribute to increasing the design efficiency and improving the inductors of the considered type. The developed technique has the universality property, as it is capable of displaying their various circuit and constructional design parameters.

Comparative analysis of electromagnetic parameters and power interactions in a large turbogenerator in asymmetric load mode

Purpose. Presentation of the results of a rotating magnetic field numerical calculation of a turbogenerator in an asymmetric load mode within its standard limitations. Methodology. The calculation of the rotating magnetic field at full rotation of the rotor is carried out by the finite element method according to the FEMM program. Calculations are automated by controlling the program using Lua script. Results. Calculations are carried out for a 325 MW turbogenerator. The temporal functions of magnetic flux linkage and the corresponding EMF of the rotor winding and phase stator windings were obtained, the power processes in the ferromagnetic core of the stator of the turbogenerator were analyzed, namely the force actions on the teeth and on the core as a whole, the pulsations of the electromagnetic moment and the time functions of its variable component. For a more detailed illustration of the results, similar calculations are performed for the symmetric load of the turbogenerator. Practical value. Analysis of the operation of the TG with an unbalanced load showed problems of power and electromagnetic nature. It is shown that the time functions of the forces acting on the teeth of the stator core are almost the same as those with a symmetrical load, but the compressive forces acting on the core have increased. It is determined that the pulsations of the electromagnetic moment reach 17% of its average value.

A Diagnosis of Stator Winding Fault Based on Empirical Mode Decomposition in PMSMs

Stator winding faults may cause severe damages in Permanent Magnet Synchronous Motors (PMSM) if not detected early on. The earliest fault detection in motors should be made during transient states throughout the initial starting period. A new approach based on Empirical Mode Decomposition (EMD) and statistical analysis was presented for detecting stator winding fault by way of transient state phase current of PMSM in this study. Models based on finite elements method were developed for the PMSM representing the healthy and faulty states in order to implement the suggested fault detection method. Afterwards, transient state stator phase winding currents were measured for healthy and faulty states under nominal load in accordance with motor models. These non-linear current signals monitored were separated into its Intrinsic Mode Functions (IMF) via the EMD method. Pearson Correlation Coefficient was used for determining the IMF that most resembles the characteristics of the main signal. Statistical parameter-based feature extractions were carried out for the IMF signals determined for the healthy and faulty states. Fault and fault level detection were carried out successfully by comparing the obtained feature vectors. The acquired results have put forth that the suggested method can be used securely for fault detection in electrical machines especially for early fault detection.

Modeling and Evaluation of Stator and Rotor Faults for Induction Motors

The modeling of stator and rotor faults is the basis of the development of online monitoring techniques. To obtain reliable stator and rotor fault models, this paper focuses on dynamic modeling of the stator and rotor faults in real-time, which adopts a multiple-coupled-circuit method by using a winding function approach for inductance calculation. Firstly, the model of the induction machine with a healthy cage is introduced, where a rotor mesh that consists of a few rotor loops and an end ring loop is considered. Then, the stator inter-turn fault model is presented by adding an extra branch with short circuit resistance on the fault part of a stator phase winding. The broken rotor bar fault is then detailed by merging and removing the broken-bar-related loops. Finally, the discrete models under healthy and faulty conditions are developed by using the Tustin transformation for digital implementation. Moreover, the stator and rotor mutual inductances are derived as a function of the rotor position according to the turn and winding functions distribution. Simulations and experiments are performed on a 2.2-kW/380-V/50-Hz three-phase and four-pole induction motor to show the performance of the stator and rotor faults, where the saturation effect is considered in simulations by exploiting the measurements of a no load test. The simulation results are in close agreement with the experimental results. Furthermore, magnitudes of the characteristic frequencies of 2f1 in torque and (1 ± 2s)f1 in current are analyzed to evaluate the stator and rotor fault severity. Both indicate that the stator fault severity is related to the short circuit resistance. Further, the number of shorted turns and the number of continuous broken bars determines the rotor fault severity.

Novel Criterion for Reluctance Torque Utility of Permanent Magnet Motors

A novel criterion for the utility of reluctance torque in permanent magnet (PM) motors is developed. The criterion, reluctance torque ratio α , can be quantified by using the PM flux linkage Ψ p of the stator phase windings, the current I , and the direct- and quadrature-axis inductances Ld and Lq , respectively. It has been shown that the conventional salient-pole ratio is not helpful in clearly judging the utility, while the ratio α can be used to make such judgements across various types of motors with different applications and outputs. Through both theoretical consideration and experiments, it has been proved that a motor with large PM flux linkage utilizes little reluctance torque even if the salient-pole ratio Lq / Ld is over 2.0 and that a large Lq / Ld increases iron loss, thus decreasing motor efficiency. We have also shown that the above-mentioned loss increase is caused by the significant superposition of q -axis flux due to the large Lq and have concluded that, in the above-mentioned case, selecting a rotor geometry with less saliency can improve the efficiency. Results are given for two types of four-pole prototype motors with an output power of 0.6 kW, a rated rotation number of 3600 min−1, and Y-connection.

Influence of asymmetrical stator axes on the electromagnetic field and driving characteristics of canned induction motor

Canned induction motors (CIMs) are particularly important for high vacuum application due to its low cost, simple design, and mechanically robust. Herein, this study reveals a mechanism of asymmetrical stator axes (ASAs) for CIMs and proposes six coefficients to describe ASA for CIMs under asymmetrical stator phase's windings. Using winding theorem, this study derived the electromagnetic field and driving characteristics in the healthy condition and ASA conditions for a 1.9 kW CIM, and analysed further using mathematical formulas and finite-element models. Both simulation and experimental results show good agreement, and significant variation was found in total harmonic distortion, the amplitude of air-gap flux density, and driving characteristics of CIMs. Further, investigation of back-electromotive force and stator current showed their efficacy as a diagnosis signature to detect the fault of ASA in CIMs. The obtained conclusions can serve as a valuable reference to design a high-performing CIMs control system.

Eliminating starting hesitation for reliable operation of switched reluctance motor without machine parameters for light electric vehicle applications

In this study, an initial rotor position estimation at standstill condition is presented for reliable operation of switched reluctance motor (SRM) without initialising machine parameters for light electric vehicle (LEV) applications. The prime objective of this method is to startup an SRM without using the mechanical position sensor, and eliminate the starting hesitation and starting jerk issues from standstill condition. In the proposed method, the initial rotor position at standstill is determined by injecting a single pulse dc voltage simultaneously into all stator phase windings for a very short period (microsecond). The obtained current envelope data is then used to calculate the initial rotor position with the quadratic polynomial interpolation technique without any prior knowledge of other motor parameters. The experimental results for a 3.5 kW, 6/4 SRM are provided to substantiate the overall good performance. The developed system can be considered as a strong candidate for high precision LEV applications.

Modelling of interior‐mount LSPMSM under asymmetrical stator winding

Reliable and safe operation of electric motors in the industry is highly desirable. Accurate modelling is the first step in developing a diagnostic tool for different types of failures. This study presents a generalised dq-model for interior-mount line start permanent magnet synchronous motors under asymmetrical stator phase's windings. The presented dq-model has been derived using winding theorem. Implementation and simulation of the derived dq-model has been done using MATLAB/SIMULINK software. For validation purposes, interior-mount line start permanent magnet synchronous motor (LSPMSM) under this fault condition is implemented using the JMAGTM-finite-element-based software. The performance of a 1-hp interior-mount LSPMSM motor under different loading levels and stator winding asymmetric conditions has been investigated using the simulated MATLAB and JMAG models. Simulation results of MATLAB and JMAG are in very good agreement and show that under asymmetrical stator winding condition, oscillations are obvious in the torque characteristics of the motor. In addition, the torque experience high oscillations at a steady state due to the asymmetry between stator phases. Finally, investigating torque frequency spectrum showed that they can be good signatures in diagnosing asymmetrical stator winding faults in interior-mount LSPMSM.