Li Junqing

Rotor winding inter-turn fault analysis of doubly-fed induction generator based on negative sequence component

Inter-turn short circuit fault is the main fault type of doubly-fed induction generator (DFIG), so online monitor and fault diagnose are particularly necessary for DFIG. However, due to the presence of the generator external imbalances, winding inter-turn fault diagnosis is difficult. Based on the finite element model, we analyzed the negative sequence current and harmonic components generated by the rotor winding inter-turn fault of DFIG. We get the features of rotor inter-turn fault in DFIG, and the fault characteristics in the case of grid imbalance.

Study of rotor winding inter-turn short circuit fault in doubly fed induction generator based on current signal spectrum analysis

Rotor winding inter-turn short circuit fault is one of the common faults of doubly-fed induction generator (DFIG), so the fault diagnosis is great necessary. This paper described the causes and hazards of the inter-turn short circuit fault, analyzed the variation regulation of the electromagnetic properties, and established a multi-loop model of DFIG in cases of fault of rotor winding inter-turn short circuit and in normal conditions. Then the multi-loop model was used to simulate 5.5kW DFIG which was in normal conditions and in cases of fault of rotor inter-turn short circuit, respectively. Fourier transformation was applied to analyze the harmonic variation of current in cases of faults, and current spectrum features was summarized. The work is significant to research new protection program, protection criterion and to improve design and manufacture.

Static state stability analysis of AC-excited generators

The most significant difference between the ac-exited generator and the traditional synchronous generator is the adjustable speed. A detail analysis of the static state stability of the ac-excited generator is present. The stability of the ac-excited generator is limit not only by the static state stability limit as synchronous machine but also by the breakdown torque as asynchronous machine. The relation between static state stability limits and rotor speed is derived from the mathematic model, thereby the law of static state stability at any speed is presented and these have been tested by dynamic physical simulative experiment.

Research on temperature-rise of stator iron-core end region of turbine generator

The heating process of stator end-region of synchronous generator on all kinds of operating conditions is analyzed. With the phasor diagram of the electric-magnetic potential in cylindrical rotor synchronous generators, the mathematical model of temperature of stator end region in synchronous generator is deduced. The relationship between the temperature of stator end region and the active power, reactive power and armature voltage is developed. The parameters of the temperature model are identified with the method of least squares. A new temperature-rise limit curve of stator end region is deduced, which is given in the P-Q operating chart of synchronous generator. The preciseness of the temperature model is validated with the experimental values of turbine generator. The model is also used to real-time monitor of the generator stator end region temperature.

FEM analysis on interturn fault of rotor wingding in DFIG

The stable operation of Doubly-fed induction generator (DFIG) is vital to wind power overall system reliability. The rotor winding inter-turn short circuit fault is one of the common electrical faults in DFIG, so it is necessary to research the fault features of DFIG with rotor winding inter-turn short circuit fault. The finite element model (FEM) of DFIG was presented and used to simulate the electromagnetic field distribution of DFIG under different degree of rotor inter-turn short circuit fault. The phase angle difference, the harmonic content of rotor currents and the harmonic content of air gap flux density were also explored. The approach presented in this paper will provide the basis for the protection of DFIG with rotor inter-turn short circuit fault.

The research of the inter-turn short circuit of the stator windings in doubly fed induction generator

The doubly fed induction generator (DFIG) is an important component of wind turbine systems. In order to identify incipient faults quickly and ensure safe operation of DFIG, this paper proposes a way to diagnose inter-turn short circuit fault at stator windings, which is based on multi-circuit theory. The mathematical model of DFIG is established in this paper and simulation of DFIG in normal operation and inter-turn short circuit fault at stator windings are carried out. A detail analysis about simulation results is presents, especially about short circuit current. By analysis, the characteristics of inter-turn short circuit fault are obtained.

Influence of stator turn-to-turn short-circuit on magnetic field of DFIG

Doubly fed induction generator (DFIG) are mainly used in wind power system where its reliability is important requirement. In DFIG, stator internal turn-to-turn short-circuit is a common fault. Analysis by Electro-Magnetic Field (EMF) modeling is very promising in detecting stator inter-turn faults in DFIG. Hence, in this paper an in-depth investigation is conducted by electromagnetic performance of a DFIG with stator turn-to-turn short-circuit. The finite element method (FEM) is used to model EMF of DFIG under various stator turn-to-turn short-circuit, this model takes into account teeth and slots effect of stator and rotor, saturation of core. It is easy to simulate different positions and degree stator turn-to-turn short-circuit conditions in DFIG by change the particular parameters. The harmonic components of air-gap flux density are studied. The model and simulated results are validated by test data of a DFIG. The approach presented in this paper will provide the protection basis for the DFIGs with stator inter-turn short circuit fault.

A thermal model for the water-cooled stator bars of the synchronous generator

The paper presents a thermal model of the water-cooled stator bars in a large synchronous generator using the equivalent thermal network method. A stator bar is studied, the copper strands and cooling water are divided into elements simultaneously and the temperature of cooling water is also calculated. Then, simple element and more elements analysis methods are used to calculate the temperature of stator bars. A stator bar of a QFQS-200-2 turbo-generator is computed with the proposed methods. The calculated and the measured results are analyzed and the proposed method is validated to be correct.

The teaching reform on the “Electrical Machinery” course offered to the “Excellence Engineer” class

“Electrical Machinery” is the electrical engineering professional basic subject featured with theory and abstract content, involving many disciplines, and closely linked with the engineering practice, which makes it hard in the teaching and learning process. Based on the “Electrical Machinery” course offered to the “Excellence Engineer” class for Electrical Engineering and Automation, the paper introduced the properties and characteristics of the “Electrical Machinery” course and discussed the teaching reform of “Electrical Machinery” course. The author included the selection of teaching content and organization, the development of teaching, selection and organization of experimental projects and curriculum appraisal way, etc.

Study on DFIG stator turn-to-turn short circuit considering control strategy

Stator inter-turn short circuit fault is one of the common faults in Double Fed Induction Generator (DFIG), the mathematical model of the DFIG is established based on the multi — loop theory, and the model of DFIG is built on the MATLAB / Simulink platform under normal condition and different degrees of inter — turn short circuit. The mathematical model of the grid side converter is analyzed to determine the corresponding control strategy, and the concrete given process of the PI regulator parameters is given. Through the simulation analysis of the DFIG under different conditions, the simulation results are consistent with the actual situation, which proves the feasibility of the control strategy. When the stator occurs turns short-circuit, the stator three-phase current is not symmetrical and its corresponding amplitude is increased, there is more obvious 90Hz specific frequency harmonics in rotor-side current FFT.