Youpeng Huangfu

Dynamic Deformation Analysis of Power Transformer Windings in Short-Circuit Fault by FEM

This paper presents the investigations of short-circuit current, electromagnetic force, and transient dynamic response of windings deformation including mechanical stress, strain, and displacements for an oil-immersed-type 220-kV power transformer. The worst-case fault with three-phase short-circuit happening simultaneously is assumed. A considerable leakage magnetic field excited by short-circuit current can produce the dynamical electromagnetic force to act on copper disks in each winding. The two-dimensional finite element method (FEM) is employed to obtain the electromagnetic force and its dynamical characteristics in axial and radial directions. In addition, to calculate the windings deformation accurately, we measured the nonlinear elasticity characteristic of spacer and built three-dimensional FE kinetic model to analyze the axial dynamic deformation. The results of dynamic mechanical stress and strain induced by combining of short-circuit force and prestress are useful for transformer design and fault diagnosis.

Transient Performance Analysis of Induction Motor Using Field-Circuit Coupled Finite-Element Method

In this paper, the application of field-circuit coupled finite-element method for predicting the performance of induction motor (IM) under a sinusoidal voltage excitation is described. The numerical analysis is performed by solving the nonlinear time-stepping finite-element equations coupled with the circuit equations and mechanical motion equations. The circuit equations are described by means of improved nodal method. The local analytical solution of Laplace equation is used to improve the precision of electromagnetic torque. The performances of both three- and single-phase IMs are simulated using the developed field-circuit coupled code. The comparison among the results calculated by the code, the commercial FE package, FLUX 2-D, and the experiment results suggests the correctness of the field-circuit coupled method and related developed code.

Optimum Design of Rotor for High-Speed Switched Reluctance Motor Using Level Set Method

This paper presents a novel rotor structure optimized by using the level set method (LSM) to improve the static torque characteristics of a two-phase 4/2 high-speed switched reluctance motor. The magnetic equivalent circuit approach is used to analyze the influence factors on the static torque. The inner material boundary contained in the rotor saliency, which will be optimized, is implicitly represented by an embedded level set function. The evolution of the inner material boundaries is driven by the normal velocity derived through sensitivity analysis and adjoint variable computation. Optimal rotor configuration produces the nonuniform distribution of magnetic flux density in the air gap at aligned position, which can make the ratio of maximum and minimum inductances increased. High-permeability material is applied to enhance the mean torque. In order to achieve the optimal static torque, the strategy combining finite-element electromagnetic computation with LSM is conducted to optimize the rotor saliency at different rotor positions. The comparison of the optimized rotor configuration using LSM with that using density-based method suggests that the optimized rotor structure obtained using this presented method is easier to implement.

Geometry and Power Optimization of Coilgun Based on Adaptive Genetic Algorithms

A coilgun is an electromagnetic launcher based on electromagnetic induction. The projectile with a heavy load can be accelerated to a high speed. The currents that flow through the driving coils and the projectile would produce joule losses. All of the properties are drastically determined by the geometry and power of a coilgun. This paper aims to optimize the geometry and power parameters of the coilgun. The muzzle velocity is selected to be the objective when the temperature rise limitations are taken into consideration. To analyze the performance, an equivalent circuit model including the calculation of temperature rises is employed. The performance of a three-stage coilgun is calculated based on this model and then this coilgun is optimized with the utility of adaptive genetic algorithm taking the influence of temperature rise into consideration. The result of optimization shows that the muzzle velocity is improved and the temperature rises are conformed to the design requirements. The optimized coilgun is simulated by the finite-element method to verify the performance.

Conducted EMI simulation for a high power Ultra-precision PMSM driven by PWM converter

The conducted electromagnetic interference (EMI) and overvoltage characteristics for a spindle permanent magnet synchronous motor (PMSM) driven by pulse width modulation (PWM) converter are comprehensively presented. The high power, ultra-precision PMSM is applied to a computer numerical control (CNC) grinding machine. The conducted EMI prediction model mainly includes multi-core shielded cable, high frequency (HF) converter and PMSM models. The multi-transmission line (MTL) theory is employed to establish the multi-core shielded cable considering their coupling effect caused by the control pairs. The parasitic capacitance for the PWM converter is calculated by using the analytical formula. The HF equivalent circuit model of the PMSM is obtained combining the methods of impedance measurement and vector fitting method. The influence of the rotor position on the PMSM impedance measurement is considered. The common mode (CM) and differential mode (DM) interference voltage and current both for the output of inverter and the input of PMSM terminals are conducted by using the prediction model. The parametric influence of the long multi-core shielded cables on the overvoltage for the PMSM terminal is discussed.

Extended Finite-Element Method for Electric Field Analysis of Insulating Plate With Crack

In this paper, the extended finite-element method (XFEM) is employed to analyze electric field of insulating plate with crack. To begin with, both the approximation of XFEM and features of the enrichment functions for crack tip are presented. Then, XFEM is used to solve electric potential of an insulating plate with a middle crack, which proves the method can save computational time by comparison with classic finite-element method (CFEM) under the same computational accuracy. In addition, XFEM is also applied to calculate electrical field at crack tip of an insulating plate with an edge crack, which reveals that the relative error between XFEM and CFEM is small when the meshing size of CFEM around crack tip is smaller than that of XFEM. Therefore, electric field analysis of discontinuous and singular solutions can demonstrate the superior performance of XFEM.

Electromagnetic-Thermal–Deformed-Fluid-Coupled Simulation for Levitation Melting of Titanium

A numerical simulation, considering the two-way interactions of the electromagnetic, thermal, and fluid fields with deformation associated during a levitation melting process, is performed using the finite-element method. Material properties dependent on temperature are applied for the simulation. In addition, surface-to-ambient radiation and phase change are considered, and the arbitrary Lagrangian-Eulerian formulation is employed to model the deformation of a metal sample during the melting process. The oscillations of the metal sample at different times are also simulated. The oscillations, melting time, deformation, and distributions of the electromagnetic-thermal-fluid fields are obtained at different moments. A general way to dynamically predict the melting process of induction heating and its performance evaluations are provided in this paper.

Modeling and Insulation Performance Analysis of Composite Transmission Line Tower Under Lightning Overvoltage

In this paper, a new non-uniform multiconductor transmission line model combining with lumped circuit elements for a composite transmission line (TL) tower under lightning strokes is established. The metal ground-wire cross arms, the metal tower main body and its bracings are modeled as equivalent horizontal and vertical TLs, respectively. The two grounding ladders are regarded as two parallel-vertical TLs considering their mutual coupling. These distributed TL parameters are calculated by analytic equations. The composite arms are equivalent as lumped capacitances determined by employing 3-D finite-element method. The lightning overvoltage analysis for a 330-kV composite tower is performed by applying the hybrid model. The incident and reflected voltages are calculated. The insulation performance evaluation for the composite tower is discussed in detail.

Surge voltage and environmental electromagnetic field analysis for HV composite transmission tower under lightning strokes

In this paper, the surge voltages of grounding system for a 330 kV high voltage (HV) composite transmission tower under lightning strokes are comprehensively presented. An equivalent distributed parameter model of the tower is established to investigate the lightning overvoltage by using EMTP program. The distributed capacitances among the adjacent two layers of cross arms, the capacitances between the lines and grounding ladders are calculated by using three dimensional (3D) Finite Element Method (FEM). The wave impedances of the ground wire cross arm, grounding ladder, and metallic tower body are determined by using the analytic equations. The lightning overvoltage calculation and comparison are conducted considering the diverse grounding configurations, such as the single-, double-, and three-ladder grounding systems. The influence of the radius of the grounding ladder on the overvoltage characteristics is analyzed. The proper grounding ladder system is determined so that the voltage between ladder and transmission lines is less than the flashover initial voltage of the cross arm. In order to evaluate the electromagnetic environment around the tower, the induced electromagnetic field at the level of 1.5 m above the ground is computed by 3D FEM. The simulated results suggest that the electric field intensity is much greater than the safety threshold of electric field intensity around the transmission lines.

Simulation and analysis for power frequency electric field of building close to power transmission lines

Based on the design demands of the 330kV overhead transmission lines, the power frequency electric field for the power transmission lines near and over the building is simulated and analyzed in this paper. The 3-dimentional (3D) Finite Element Method (FEM) is employed to analyze the distribution of the electric field at the level of 1.5m above the ground around and inside a typical building model. The influences on electric field distribution of building located near and under the line are considered. A three-floor building model, which can be constructed with different materials, is proposed. The computational results show the shielding effect on the electric field distribution of the building and large electric field distortion near the outline of the building. The influence on the electric field intensity of the material of the building, the transmission line height, the number of the floors and the orientation of the window is respectively discussed, which can provide important references for the design and construction of the power transmission lines.