Stator End Windings Research Articles

Fatigue Propagation Characteristics of Insulation Crack Failure in Stator End Winding for Large Traction Motor Based on Magnetic–Thermal–Mechanical Coupling Model

Fatigue Propagation Characteristics of Insulation Crack Failure in Stator End Winding for Large Traction Motor Based on Magnetic–Thermal–Mechanical Coupling Model

Mechanical properties and insulation damage of PMSG stator end windings with eccentricity considerations

The mechanical properties and insulation damage of stator end windings in permanent magnet synchronous generator (PMSG) are investigated by theoretical analysis, finite element analysis (FEA) and experiment verification. First, a theoretical model of the winding electromagnetic force (EF) and vibration response before and after eccentricity faults are established. Then, the stress/strain distribution of the end windings under different working conditions is analyzed. Finally, the insulation damage behavior of end windings with initial cracks is studied and characterized using the stress intensity factor (SIF). The results indicate that the winding EF and vibration responses vary under different faults. The stress/strain at the joint of the winding is the largest, and the insulation layer has the maximum stress/strain under the same section. Additionally, the SIF amplitude of the crack at the winding joint is the largest. And the SIF amplitude of the crack will increase with the increase of fault degree/crack depth/crack length. The contribution of this paper lies in the comprehensive analysis of the winding EF distribution, vibration response, stress and strain, and insulation damage before and after eccentricity. This analysis can provide valuable reference for the health monitoring of PMSG eccentricity faults and the prevention of winding insulation damage.

Simulation of the Circulating Bearing Currents for Different Stator Designs of Electric Traction Machines

Pulse–width modulated inverters are commonly used to control electrical drives, generating a common mode voltage and current with high–frequency components that excite the parasitic capacitances within electric machines, such as permanent magnet synchronous machines or induction machines. This results in different types of bearing currents that can shorten the service life of electric machines. One significant type of inverter–induced bearing currents are high–frequency circulating bearing currents. In this context, this work employs finite element analysis and time-domain simulations to determine the common mode current and circulating bearing current for various permanent magnet synchronous machine designs based on the traction machines of commercial electric vehicles with a focus on the stator. The results suggest that the ratio between the circulating bearing current and common mode current is much smaller in permanent magnet synchronous machines for traction applications than previously established in conventional induction machines, with values below 10% for all analyzed designs. A further increase in the robustness of such electric machines to the detrimental effects caused by the inverter supply could be achieved by reducing the parasitic winding–to–stator capacitance or by increasing the stator endwinding leakage inductance.

Analysis of PMSM NVH performance in electric propulsion systems using FE models

The stator of the PMSM is the main transfer path for the Electro Magnetic (EM) force from stator teeth to the drive unit (DU) through its mounting ears. First, a FE model of full winding stator model along with connection ring is analyzed for modal behaviors. Time domain EM force excitations are converted into frequency domain and applied at the stator teeth. This enables stator mounting forces analysis at all critical NVH orders. Next, the detailed FE modelling approach is compared with response calculated form a simplified modelling approach, with stator end windings modelled as lumped mass and inertia to reduce computational time. The comparison study of two approaches clearly shows the benefits of using simplified FE models for studying motor whine with reduced modelling and computational costs. Furthermore, the frequency-dependent stator damping measured from modal test is applied in electric DU analysis to evaluate NVH performance excited by motor EM force excitations using simplified stator model. The sound power level radiated from the DU and the mount vibration response show negligible influence of stator damping at DU unit level NVH response in the low frequency range. Analysis and test results correlate reasonably well at the dominant motor whine orders for the DU, which validates the proposed method.

Fracture failure analysis of insulation with initial crack defect for stator end-winding in induction motor by using magnetic-structural coupling model

The insulation mechanic failure in stator end-winding of induction motor is usually an early and serious cause to weaken the residual breakdown electrical field strength and produce the short-circuit fault, especially subjecting to the combination of dynamical electromagnetic forces, mechanical stress and vibration. In this paper, the fracturebehavior of insulation layer with considering the initial crack defects and end-hoop support failures in end-windings were analyzed by using magnetic-structural coupling model and finite element method (FEM). Firstly, the distributions of magnetic flux density and electromagnetic force around the stator end region were determined by injecting three-phase alternating current. Secondly, the dynamic characteristics of deformation, stress and strain in winding insulation were respectively calculated by coupling the transient electromagnetic and structural analysis. Furthermore, the weak points of the concentrated stress and strain were located. Thirdly, the crack model mounted in winding insulation is defined and simulated by employing three-dimensional (3-D) semi-elliptical crack element. To evaluate the fracture mechanism and the degree of crack expansion quantitatively, the stress intensity factor (SIF) was introduced. Finally, the influence of crack location, direction, depth and end-hoop support failure on SIF and crack propagation were investigated. Results show that the concentrated stress at knuckle part of the coil insulation is lager quite larger than that of other parts. The SIF of transverse crack is larger than that of longitudinal cracks. The larger the initial crack depth in the stator end-winding insulation, the more serious the tendency and degree of crack fracture. Local end-hoop support failure also has an important influence on the crack propagation. Results in this study may contribute to the understanding of fracturefailure behaviors in insulation under dynamical electromagnetic vibration and provide necessary theoretical reference for fault diagnosis and prediction of stator winding in induction motors.

Stator winding hotspot temperature rise characteristic study of an axially forced air-cooled motor with air deflector

A ventilation system with an air deflector is suggested to enhance the cooling of the stator windings in an axially forced air-cooled motor. The global fluid and thermal evaluations are carried out using the numerical analysis method. The simulation results are verified through experiments, and the relative error between the two sets of data is 4.4%. Then, the fluid flow and heat exchange behavior within the motor are studied in relation to the placement of the air deflector. When an air deflector is installed at the air outlet side end region, the air is directed to collide with the stator end winding, thereby promoting convective heat exchange on the stator end winding surface. Additionally, numerical analysis is employed to investigate how the position and geometric features of the air deflector affect the variation in the stator winding temperature rise and overall pressure drop. Shortening the distance between the air deflector and the cooling duct and the stator end winding is conducive to further improving the cooling. Furthermore, it is established that the maximum and average temperature rise of the stator winding may be reduced by 8.9 K and 8.2 K, respectively, when using the proposed air deflector.

Aerodynamic Design of Cooling Guide for Electrical Machine in Electric Ducted Fan

Abstract Electric ducted fan has newly emerged as the most compact type of propulsion fan for flying cars, because of its flexible configuration arrangement, low noise level and high safety level operation. Typically, an electric ducted fan is composed of a hub-driven fan and a hub-mounted inner rotor electrical machine. The thermal management of the hub-mounted electrical machine is essential because it determines the machine's continuous output power and reliability, as well as the fan thrust force. The heat transmitted from the stator winding to the cooling guide vane (CGV) is dissipated by introducing the air flow at hub region to the CGV. Therefore, in order to better improve the thermal performance of the CGV, an aerodynamic design of CGV is proposed in this paper for better thermal management of stator end-windings. First, for a certain desired power output of electrical machine under temperature constraints of stator winding, lumped thermal network is established to derive the requirement of heat transfer coefficients of the CGV. Then, from engineering feasibility, three different CGVs including straight type, arc-shape type and airfoil-shape type are tested by computational fluid dynamics. The evaluation of the CGV designs include the flow characteristics, power requirements, and thermal characteristics for stator winding cooling purposes. In comparison with the conventionally straight type CGV, improvements are gained from the designed arc-shape type and airfoil-shape type cooling configurations, whereas the fan thrust force remains the same simultaneously. It is verified that the arc-shape type and airfoil-shape type CGVs are promising in enhancing the thermal management performance of the electrical machine stator winding without power requirement.

Thermal Benefits of a Cooling Guide Vane for an Electrical Machine in an Electric Ducted Fan

Equipped with a distributed electric propulsion system, eVTOL is the primary vehicle for future urban air mobility. The electrical machine determines the weight of the distributed electric propulsion system, and the cooling capability determines the electrical machine’s weight. The electrical machine with air cooling is preferred for eVTOL due to its simplicity and light weight. This paper presents a new air-cooling system for an electrical machine in an electric ducted fan propulsion system. The novel cooling system consists of a cooling guide vane with a heat pipe (CGVHP), which is located downstream of the ducted fan rotating blade. The heated end of the heat pipe is inserted into the stator end windings and the cold end is inserted into the cooling guide vane. The heat generated in the windings is transmitted to the cooling guide vane by the heat pipe and dissipated by the forced convection using low-temperature air passing through the ducted fan. The cooling performance of the cooling guide vane with the heat pipe was numerically simulated, considering several critical design factors. The simulation results showed that the proposed CGVHP can be helpful for reducing the winding temperature of the electrical machine by over 25.5 °C at the peak power condition of 15.7 kW.

Multi-objective optimum design of five-phase squirrel cage induction motor by differential evolution algorithm

Compared with the traditional induction motors, five-phase squirrel cage induction motor (FSCIM) have the advantages of lower torque ripple and single-phase power, flexible control strategy, higher power density and fault-tolerant operation, which has been widely applied on electrical vehicles, rail transit, underwater vehicles and so on. This paper presents an analytical design optimization method based on the coupling of electromagnetic equivalent circuit (EEC) and differential evolution algorithm (DEA). Furthermore, the difference between three and five-phase winding on harmonic specific leakage permeance is investigated in detail. The nonlinear and oeolotropic influences of design geometrical parameters (slots openings, main dimension ratio, yoke height, airgap length, etc.) on the performances of the basic FSCIM model are evaluated with analytical model. For more accurate results, the harmonic characteristics of five-phase winding structure, iron core saturation, rotor slot skew width, stator end winding, slot leakage inductance and stator and rotor slot structure are considered. Meanwhile, the efficiency, power factor, maximum torque, slot fill factor and material consumption of FSCIM are calculated as the comprehensive objective function. The transient finite element analysis (TFEA) and experimental test verify the accuracy of the proposed optimum model. In addition, the feasibility of the multi objective optimization design scheme provided by the analytical model is verified by TFEA.

Impact of Radial Air-Gap Eccentricity on Stator End Winding Vibration Characteristics in DFIG

In this paper, qualitative theoretical derivations, finite element analysis (FEA) and experiments are used to investigate the electromagnetic force (EF) and vibration characteristics of end windings. In contrast to previous studies, this study focuses not only on end winding EF/vibration under normal and radial static air gap eccentricity (RSAGE) conditions, but also for the cases of radial dynamic air gap eccentricity (RDAGE) and radial dynamic static hybrid air gap eccentricity (RHAGE). Firstly, the magnetic flux density (MFD) is derived for normal and radial air gap eccentricity (RAGE) faults, and detailed EF expressions are obtained before and after the RAGE fault. The finite element analysis (FEA) and experimental studies were performed on a four-pole DFIG at a speed of 1500 rpm to verify the proposed theoretical analysis. It is shown that RSAGE only enlarges the EF/end winding vibration and does not introduce new frequency components. RDAGE not only increases EF/end winding vibration but also introduces new frequency components. RHAGE can be seen as a superimposed effect of RSAGE and RDAGE.

Experimental Modal Analysis of Induction Machine Stator End Windings of Driving End and Non-Driving End to Predict the Looseness

Experimental Modal Analysis of Induction Machine Stator End Windings of Driving End and Non-Driving End to Predict the Looseness

Dynamical characteristics and influencing factors of stator end-windings of a turbine generator analyzed via heterogeneous element fusion modeling

The power output rating of a turbine generator is affected directly by efficient cooling, especially near the stator end-windings. However, modeling the coolant flow through the stator end-windings of a high-powered generator remains challenging because of the many parts with irregular geometries and the intricacy of the cooling flow paths.In order to study the dynamical characteristics of stator end-windings, the finite element modeling of the stator end-winding with beam element, shell element and solid element has been established based on the analysis of different types of structural components. Further, a large number of modal calculations under different considerations including modulus of elasticity, boundary condition, connection area, position and temperature have been carried out.The frequency of the elliptical mode at the turbo-generator end was 81.5 Hz, and that at the exciter end was 77.2 Hz. The errors from the test average were 1.62% and 3.34%, respectively. The results showed that the FEM of the TG stator end reflects the vibration of the actual prototype precisely. The laws of natural frequencies with respect to different circumferential spacer blocks, radial pressure plate, external boundary conditions, spring-plate connection area, positions of spacers between bars and temperature including have been clarified.The structure of the stator end is complex, and researches continue into its dynamic characteristics with much work remaining. (1) Some more complex factors such as preload will be added to the model, and the influence of multiple factors on the vibration characteristics have been analyzed. (2) When using multi-point binding constraints, setting of the pinball region has a significant impact on calculation results. There is currently no fixed conclusion on how to set a reasonable PINBALL area size. (3) The mechanical properties of the end insulating material will change with the increase of temperature, but the trends cannot be predicted accurately.

Effect of Static Rotor Eccentricity on End Winding Forces and Vibration Wearing

In order to study the vibration wearing regularity and the strength failure point of stator end windings before and after static rotor eccentricity, the three-dimensional electromagnetic forces and the subsequent mechanical responses are studied in this paper. The electromagnetic force, stress, and deformation on the end winding of the QFSN-600-2YHG turbo-generator are calculated by the finite element method (FEM) through an electromagnetic-structure coupling. The radial vibration characteristics of the winding are verified by experiments. It shows that the vibration wearing in the same layer is more serious than that between two neighboring layers. For different layers, the interphase coils endure a larger wearing risk than the innerphase coils. Inside the same phase, the last coil along the rotating direction has the highest risk of insulation wearing. The occurrence of static rotor eccentricity will significantly increase the electromagnetic forces and the vibration amplitudes on some coils. The end-phase coil which is close to the minimum air-gap point is the most dangerous one due to the lasting overstresses and the intensified deformations.

Coupled Electromagnetic-Fluid-Thermal Analysis for End Zone With Electric Screen in Large Water-Hydrogen-Hydrogen Cooled Turbine Generator Under Different End Winding Extensions

Extension lengths of the stator and rotor end windings will obviously affect the electromagnetic field, fluid flow, and temperature of end components in the end zone of large water-hydrogen-hydrogen cooled turbine generator. In this paper, a 330 MW water-hydrogen-hydrogen cooled turbine generator is analyzed. Flow network of this turbine generator is established. The fluid velocity and the pressure (boundary conditions) are obtained at the different positions of this turbine generator after solving the equations of flow network. Three-dimensional transient electromagnetic field is calculated in the turbine generator end zone. The leakage magnetic field and the losses (heat source) of end components are determined in the turbine generator end zone under the different lengths of stator and rotor end winding extension. Based on these results, three-dimensional fluid-thermal coupled model is given in the end zone. The distribution of complex fluid velocity in the turbine generator end zone is determined. The temperature distribution of the stator end winding, clamp plate, electric screen, and finger plate is studied under the different lengths of stator and rotor end winding extension. The calculated temperature results agree well with the measured values.

Parameter Identification Based Online Noninvasive Estimation of Rotor Temperature in Induction Motors

This article proposes a rotor temperature estimation method for in-service induction machine (IM) based on parameter identification, which combines the advantage of recursive least squares (RLS) and model reference adaptive system (MRAS). The RLS with forgetting factor is firstly adopted to identify the parameters of motor inductances. Then, the online identification of rotor resistance can be realized via the MRAS based on the instantaneous reactive power (IRP) and the proportional integral (PI) regulation adaptive law designed by the Popov hyper-stable theory. Thereby, the rotor temperature is computed by the resistance-temperature relationship of metals. To achieve a fast convergence of the parameter identification, rotor slot harmonics are extracted from the stator current and used to determine the rotor speed in real time. Furthermore, to obtain a more accurate initial value of the stator and rotor leakage inductances and resistances, the first 5–15 cycles of the IM starting process are used to mimic the locked-rotor test condition. A merit of the proposed method is that it requires significantly less time to estimate the rotor resistance than the traditional methods. With a novel test bench, experimental validation is performed on a 22-kW IM. In the test, the rotor temperature is measured in three different ways: 1) wireless sensors inserted in the rotating rotor core and rotor end rings, 2) infrared sensor for rotor end ring temperature, and 3) PT100 installed in stator end winding. With this test bench, the real rotor temperature was revealed, and the effectiveness of the presented method is also verified.

Stator End-Winding Thermal and Magnetic Sensor Arrays for Online Stator Inter-Turn Fault Detection

In this paper, two novel stator inter-turn fault sensing schemes, based on infrared (IR) thermopile sensor array (IRSA) and Hall-effect sensor array (HESA) are proposed. These circular sensing arrays are mounted along the inner wall of the stator's casing facing the end-winding region. This enables a direct measurement of temperature and magnetic flux distribution along the end-winding region in a non-contact way. Thus, the deviation in thermal and magnetic symmetry introduced by an inter-turn short circuit fault can be readily assessed. The proposed sensing schemes provides an intuitive and straight forward approach to inter-turn fault monitoring compared to the conventional methods, which depend on detecting fault induced secondary effects on external signals (motor currents, casing vibration, and temperature). The practicality and the diagnostic ability of the end-winding sensor array approaches in detecting the stator inter-turn faults is demonstrated using a 1.5 kW induction motor test rig. Compared to IRSA, HESA is found to be more versatile and with better early fault detection capability. Hence, an embedded online monitoring algorithm based on HESA is developed and demonstrated using the test rig.

Modal Analysis of Three-dimensional Model of Turbogenerator Stator End Windings

Concerning the structural complexity of large-scale turbogenerator stator, this research aims at establishing the windings model of the large-scale turbogenerator stator ends by using ANSYS, including the ends of upper and lower condutor bars, spacer blocks between adjacent condutor bars, and inter-layer rings between the upper and lower condutor bars. Moreover, the modal analysis of the stator end windings was performed with the help of ANSYS, and the parameterized finite element analysis was further conducted on the space blocks that may affect the overall structural mode and natural frequency of the ends, and the influence trend of the space blocks on the natural frequency of the elliptical mode was obtained. It provides a reference for the design of the generator end structure and its improvement, and also provides a basis for the subsequent research on the electromagnetic vibration of the end windings and the stator windings.

Influence of the Stator Winding Vibration on the Insulation System Lifetime

<span lang="EN-GB">The article deals with establishing of natural frequencies at the stator endwinding in stage of design of the machine (generator) and then measurement of the mode shapes (modal analysis on a real machine).</span>

Performance Analysis of Outer-Rotor Single-Phase Induction Motor Based on Magnetic Equivalent Circuit

Single-phase, outer-rotor squirrel cage induction motors are widely used in ceiling fan applications. Furthermore, they can be employed for pumps, and in-wheel hub drives. In this article, an analytical model based on magnetic equivalent circuit is proposed to evaluate the performance of the motor. The influence of rotor slots' skewing, stator end windings, slots' leakage inductance, and core saturation are included in the model. Furthermore, the windings' copper losses and the core's iron losses are calculated using the proposed model. The results of the presented model are compared with those of time variant finite element analysis (TVFEA) and experimental measurements close agreement between the results confirms the success of the proposed model from accuracy point of view. Furthermore, the computation time required for the proposed model considering the linear and nonlinear cores are 1 min and 11 min., respectively. However, those of TVFEA considering 64 000 mesh elements for linear and nonlinear cores are 21 h and 28 h, respectively.

Analysis of air flow and heat transfer in a winding using porous medium approach

Abstract The efficient cooling of turbo-generators especially in the end-windings region directly affects the power output rating. Modeling the coolant flow passing through the stator end-winding of a high-powered generator, however, remains a challenge due to a large number of parts with irregular geometries as well as the intricacy of cooling flow paths. This paper focuses on a numerical investigation of flow and heat transfer in stator end-winding aiming at replacing the geometry of winding with a porous medium model. Using computational fluid dynamics analysis to examine the viscous and inertial contributions to the pressure drop of airflow in the stator end-winding region, a generalized porous medium model is developed for the real physical geometry of winding together with a correlation for interfacial Nusselt number. The results indicate that the inertial effect considerably prevails over the viscous effect, that is, viscous contribution becomes small and almost negligible. It is shown that not only the pressure drop characteristics match closely within both real and porous models, but also the heat transfer results agree as well which means that the replaced porous model can amply describe the macroscopic behavior of the winding.