Hailin Li

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.

A New Interpretation of FRA Results by Sensitivity Analysis Method of Two FRA Measurement Connection Ways

As a reliable and non-destructive technique, frequency response analysis (FRA) has been widely recognized for transformer winding deformation detection and assessment. In this paper, frequency response functions (FRFs) are obtained by two different FRA measurement connection ways, namely, end-to-end voltage ratio (EE) and transfer voltage (TF) ratio measurements. At the same time, according to the two ways, sensitivities of the FRFs to electrical parameters of the equivalent circuit model of the transformer winding are investigated. Based on Tellegen theorem, adjoint network method is derived to calculate the values of the sensitivities of FRFs to electrical parameters. Meanwhile, the sensitivity characteristics of circuit parameters are studied. In addition, by comparing the sensitivity results of the two ways, the variation laws of the sensitivities under the two different connection approaches are determined. Besides, this paper can provide a new and objective method to interpret the FRA results and give us a better understanding how much the parameter variations can influence the FRA measurement results.

Cumulative Deformation Analysis for Transformer Winding Under Short-Circuit Fault Using Magnetic–Structural Coupling Model

It is inevitable for power transformers to suffer from multiple impacts of short-circuit (SC) current and huge dynamic electromagnetic force in service, which may cause large elastic and plastic deformations. Under the SC fault, the distribution of flux leakage and the amplitude of electromagnetic force may be disturbed by winding deformations or displacement. This paper analyzes the cumulative strain-stress characteristics of transformer windings using a coupled electromagnetic-structural analysis solution. The dynamic electromagnetic force, mechanical stress, and plastic deformation are calculated by the 3-D finite-element method. An example of a two-winding 110-kV transformer is simulated. It is found that an initial and slight deformation in windings may influence the magnetic flux distribution. The changed flux density may enlarge the applied electromagnetic force in the windings. The cumulative model and simulation results of this paper may be useful for investigating the winding deformation state prediction.

Simulation analysis and development of industrial design software of phase-shifting reactor used in the 6-phase rectifier system

Phase-shifting reactor (PSR) can be used to solve the harmonic problems caused by rectifiers. In this paper, according to the active power balance principle, the relationships among DC current of load, currents of power supply side, as well as capacity of core limb are built, and the design specifications of winding and core are obtained. simulation of 6-phase rectifier system with PSR by the equivalent circuit method is applied, meanwhile, the coupled circuit-field method when considering the magnetization curve is adopted. The current waves of phase A and DC side which gotten by two methods are similar, and these waves reveal that the designed PSR meets the requirements of phase-shifting angle and load. In addition, a software which can realize the industrial design and automatic simulation is developed to easy the manufacture. Lastly, the efficiency of PSR and influence of load variation on phase-shifting angle are revealed.

Mechanical characteristics analysis of defective transformer windings under short-circuit fault using 3-D FEM

Mechanical characteristics analysis of normal and defective transformer windings with eccentric distance under short-circuit (SC) fault are conducted using three-dimensional finite element method (3-D FEM). The change characteristics of maximum stress and displacement of defective windings with different eccentric distances of high voltage winding are obtained. It is found that the increase of the eccentric distance of high voltage winding may cause the maximum Von Mises stress of the windings rises under the short-circuit fault. But the eccentric distance has less influence on the maximum displacement of the winding, comparing with that influence on the maximum Von Mises stress of the windings. The results can provide reference for the design and maintenance of transformers.

Core losses calculation of nanocrystalline alloy high frequency transformer considering magnetic hysteresis effects

Core losses of nanocrystalline alloy high frequency transformer (HFT) are calculated by adopting the finite element method with magnetic hysteresis effects considered. A normal Preisach model is used to represent the magnetic hysteresis during the numerical simulation. The normal Preisach model features with simple formulations and easy parameters identification. A dynamic circuit model of laminated magnetic cores for high frequency operation is used to calculate the core losses. Results are compared between the finite element method (FEM) and magnetic circuit method to prove the accuracy of finite element method, and it also provides a more accuracy way and general to compute the core loss of magnetic cores.

Macro-modeling and passivity enforcement for PMSM winding

Purpose The purpose of this paper is to implement the macro-modeling and passivity enforcement for the equivalent high frequency circuit model of a single-phase winding for an alternating current (AC) three-phase motor. It provides a stable and strictly passive Foster-type circuit macro-model for the winding. Consequently, a stable circuit network is guaranteed when it is connected with an external passive circuit. The equivalent circuit is validated on a three-phase permanent magnet synchronous motor. Furthermore, the corresponding three-phase windings macro-model could be obtained accordingly. Design/methodology/approach The following techniques are used: the least square method, vector fitting method, the fast residue perturbation method, circuit synthesis, sequence quadratic programming method and simulated annealing method. Findings This work presents an effective approach to model an equivalent high frequency circuit macro-model for a single-phase winding. Simultaneously, both the characteristics of port passivity and component passivity are guaranteed. Originality/value This paper carries out both the port passivity and the component passivity enforcement for a single-phase winding of a motor during the macro-modeling procedure. This equivalent motor winding model can be applied to obtain the conducted electromagnetic interference and the overvoltage performance analysis for an adjustable speed motor drive system.

Titanium droplet formation in electromagnetic levitation melting process

This paper simulates the melting process and liquid titanium droplet formation in electromagnetic levitation melting (EML) process by using the finite element method. The modelling of the physical EML process involves the coupling of electromagnetic, thermal, and fluid flow fields. The bidirectional interactions of different fields are also consided. The electrical parameters, such as frequency, current, and number of turns of the excitation coils, which might affect the size of droplet, are studied. The arbitrary Lagrangian-Eulerian formulation is employed to model the deformation of metal sample during the melting process. The results show that the method adopted in this paper could dynamically predict the melting process, and size of the droplet could be controlled by modifying the electrical parameters.

Stress-based variable phase-shifting reactor for the multi-phase rectifier system

Maintaining the harmonic current suppression level of the rectifier system with different DC loads is significant. This paper presents a stress-based variable phase-shifting reactor based on the magnetostrictive effect of Galfenol, the inductance of PSR can be variable and steerable. The 3D finite element model of stress-based PSR is built, the magnetic flux distributions in the core of PSR and Galfenol, and the input-output characteristics of PSR are analyzed by the coupled circuit-field method, respectively. The relationships among the force applied on Galfenol, the inductance of PSR, the DC loads and total harmonic distortion in the 6-phase rectifier system are also studied and revealed by the simulation.