Luo Yingli

Finite Element Analysis of Field Distribution and Characteristic Performance of Squirrel Cage Induction Motor with Broken Bars

This paper develops the foundations of a technique for diagnosis and characterization of effects of broken bars in squirrel-cage induction motors based on the time-stepping coupled finite-element approach. These studies are performed by using the model to compute healthy case, one-broken-bar fault, and two adjacent broken bars fault performance data, which contains stator starting current waveforms, the current density on the bars, the magnetic force distribution on the rotor bars, and the distribution of magnetic field. Meanwhile, the iron core loss distributions on the rotor tooth adjacent to broken bars are computed, and the harmonic component of air-gap flux density is analyzed. From this data, the faulty signatures are extracted. Theoretical approach together with experimental results derived from a two-pole 1.1 kW induction motor confirms the validity of the proposed method. Furthermore, this method, which could help to develop diagnostics of broken bars and performance evaluation of induction motors, has great potential in future applications

A Design Method for Cage Induction Motors With Non-Skewed Rotor Bars

To overcome the influence of the skewed rotor bars on the operating performance of the cage induction motors, this paper presents a design method for non-skewed small and medium cage induction motor based on the time-stepping finite element method, in which the approaches of asymmetrical rotor slots, closed slots, reasonable slot combination, and air-gap length are adopted and studied systematically. With this method, the cage induction motors with non-skewed rotor bars can be realized. Simultaneously, the slot harmonic, which is caused by slot opening, can be eliminated effectively and the starting performance can also be improved. The design example on a 5.5 kW cage induction motor is presented and the experimental validation is also performed.

Computer modeling of rotating magnetic fields for teaching purpose

This paper proposes a teaching model and corresponding teaching strategy for rotating magnetic fields in AC machines, which describes the principles and characteristics of the rotating magnetic fields considering the cognitive features of students. For building the teaching model of rotating magnetic fields, the animation, visualization and man-machine interaction are comprehensively used to represent the space structure of magnetic path and windings of AC machines, variation of currents and magnetic fields with time and their space distribution and, especially, the principles and features of rotating magnetomotive force (MMF) in AC machines. It has been shown that students can more easily understand the complex and abstract concepts using the new teaching model.

The influence of wye and delta connection on induction motor losses taking slot opening and skew effect into account

As a basic theoretical research for the ultra efficiency motor design, in this paper, the influence of wye and delta connection on induction motor losses is focused on. The Multi-slice field-circuit coupled time-stepping finite element method (T-S FEM), taking slot opening and skew effect into account, is used to predict the losseswith wye and delta connection under different load conditions respectively. It is shown that the copper loss is higher when delta connection is adopted and the iron losses of wye connection may be more than that of the delta connection.

Visualization and interactive experiment of some electromagnetic problems considering cognitive features of Chinese students

This paper presents visualization and interactive experiment methods for some electromagnetic problems in electrical engineering education considering cognitive features of Chinese students. Visualization technology and interactive experiments are comprehensively used to represent the space structure of electromagnetic equipment, procedure of model creation and reasoning process, variation of currents and magnetic fields with time and their space distribution, the decomposition and resultant of the air gap magnetic field and, especially, the principles and features of rotating magnetic motive force (MMF) in AC electric machines. It has been shown that using visualization and interactive experiment technology, the students can more easily understand the complex and abstract concepts, so the teaching effect can be greatly enhanced.

Study on the operation behaviors of saturated synchronous generators considering the effect of multiple factors

In the paper the measurements to increase the calculation accuracy of synchronous generator parameters by using the finite element (FE) method are studied in detail at first. Then, through a lot of calculations, a series of curve families of a 30 MW turbogenerator are obtained, including saturation power-angle curve, magnetizing characteristics corresponding to different power angles and the curves of saturation parameters versus some operation conditions. These curve families reflect the effects of multiple factors and cross-magnetization on saturation.

Influence of Different Practical Models on the First Swing Stability of Turbine Generators

Abstract There are two popular practical models of synchronous generators used in power system simulation, both based on Park equations, defined as assumed A and assumed B respectively, according to the different assumptions. To study the influence of the different models on the first swing stability calculation precision, the physical essence of the two assumptions are revealed in theory, and it is obtained that assumed A takes account of the mutual leakage flux linkage between field and damping windings and neglects the self-leakage flux linkage of damping winding, the opposite of assumed B. Taking a 300-MW turbine generator as an example, first swing stability limits calculated by two practical models are compared; simulation results are verified by the time-step finite-element model. The influence of line reactance and excitation system on first swing stability limits is studied. Results show that the first swing stability limit calculated by the practical model with assumed A is closer to the result of the time-step finite-element model, since assumed A takes account of the larger mutual leakage flux linkage. Therefore, the practical model with assumed A is more accurate. The result provides reasonable reference to select synchronous generator models in power system simulation.

A Multifunction Energy Saving Device with a novel power-off control strategy for beam pumping motors

Based on the analysis of the measured load curves of more than 300 beam pumping motors in China, a novel power-off control strategy is proposed in this paper, which makes full use of down-stroke potential energy and includes two novel control technologies, namely, automatic tracking load variation and rapid soft re-switching of power source. Meanwhile, considering the complicated load condition, a Multifunctional Energy Saving Device (MESD) is developed. It not only contains the novel power-off control strategy but also integrates the improved wye-delta automatic conversion and auto-reactive power compensation, so that it can be used for any beam pumping unit. Furthermore, the application of the MESD in Daqing oil field is also introduced. In the past four years, the energy saving rate of more than 535 trial Devices is in the range of 10–25%.

Time-stepping finite element analysis on the influence of rotational flux on local core losses of AC electrical machines

Purpose – The purpose of the paper is to study the influence of rotational flux on local core losses of the motors, which is difficult to distinguish the iron losses caused by rotational flux in certain electric machines through experiment. Therefore, time-stepping finite element method (T-S FEM) is used to consider the rotational flux and to predict the local core losses. Design/methodology/approach – Time-stepping finite element method. Findings – It is found that, in stator side, rotational flux mainly exists in tooth root and yoke area near the bottom of stator slot, those area is about 45 percent of total stator core area; in rotor side, due to slot harmonic field, the rotational flux mainly exists in the tip of tooth. Originality/value – Through analyzing the magnetization characteristics at different positions in stator and rotor cores by T-S FEM, the influence of rotational flux on local core losses of AC electric machines is studied.

Two main factors to the effect of nonlinear characteristics of turbo-generator

By the means of finite element method (FEM), the nonlinear characteristic curves and magnetic field distribution of a 300 MW turbine generator under normal or abnormal operating condition are obtained, it is found that the iron saturation and magnetic field distortion are two main factors which cause the nonlinear phenomenon. When the power angle is given, different exciting currents will result in different magnetic leakage field distribution and as a result affect the rotor iron saturation degree. Thus in order to produce a certain E delta, the required value of resultant current ISigma will vary with the change of saturation status; besides, with a large power angle, the magnetic field distortion will lengthen the air-gap part of the main magnetic path and then influence the value of air-gap voltage Edelta