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— In this article, the finite-element method is used to study the impact on a generator's electromagnetic torque by the position and level of a rotor winding interturn short circuit. The rules involving changes to the exciting current and the reactive power of generators are analyzed under the given adjustment patterns. The results of this study show that the saturability of ferromagnetic materials reduces the torque undulations that occur during the rotor winding interturn short circuit fault and that it improves the static stability of generators. Both the simulation experiment and the real case of a rotor winding interturn short circuit demonstrated that when a rotor winding interturn short circuit happens in a turbine generator, the generator can maintain its static stability by adjusting its state variables. This results in an increased exciting current and a decreased reactive power. The analytical method described herein allows accurate prediction of the change limits of the exciting curren...

Firstly, the magnetic motive force distribution of the steam turbine generator excitation windings was analyzed, and the mathematic model of MMF was established. Then the change of MMF caused by rotor inter-turn short circuit was examined, and the MMF after inter-turn short circuit happens as the superposition of the normal MMF before inter-turn short circuit happens and the MMF produced by short circuit turns with opposite excitation current. As the former is completely symmetrical, only the opposite MMF produced by short turns was analyzed, and harmonic components with various orders were gained by Fourier analysis. The electromotive force induced in stator windings was got considering the air-gap eccentricity, and the theoretical deduction illustrate that the eccentricity has no influence on the induced electromotive force of the stator windings. The three-phase symmetrical currents of the stator produced a new revolving magnetic motive force, and induced harmonics in rotor windings, whose characteristic spectrum differs from that in normal conditions. The theory was validated by experiments at last and the method that employs harmonics detection to diagnose the inter-turn short circuit malfunction of the steam turbine generator was established.

The characteristics of the stator winding parallel-connected branches circulating current are first analyzed, which is the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the size and the distribution of circulating current are associated with severity of the short circuit. Next, the virtual instrument for the rotor winding inter-turn short circuit fault is designed based on LabVIEW and the data acquisition card PCI-6251, which consist of the data analysis and data processing module, the fault characteristic extract module, the data text storage module, the data and curve display module, the database management module, the Off-line system and help system and the system configuration module. Finally the virtual instrument is successfully applied to SDF-9 fault simulation generator.

As the structure of generator is complex, and the saturated magnetic field is nonlinear, it is difficult to use generator's mathematic model to calculate field current directly, and then hard to use the deduced method to identify rotor interturn short-circuit fault, the computation time is long, and the computation precision is not good, so it is difficult to diagnose online. We proposed a new Radial Basis Function Network (RBFN) in this paper, it is two levels iteration clustering algorithm. This method overcomes the shortcomings that other algorithm have, it can compute the nerve unit number, center and width of RBSN implication layer automatically, and the clustering result is more reasonable, consequently increase the precision of RBSN. In condition of not adding any equipment, using actual measured inactive power, active power and terminal voltage etc. electric parameters of QFSN-300-2 generator as input, and in virtue of self-adaptive RBSN to identify generator field current, combining rotor inter-turn short-circuit fault diagnosis model to identify rotor inter-turn short-circuit fault online, it is faster than simply use generator mathematic model, and has high precision. After certification, the result is: comparing to the traditional diagnosis model, it increases the diagnosis precision and speed greatly, and satisfies the need of online identification.

Generator vibration characteristic and electric characteristic are analyzed when the rotor winding inter-turn short circuit fault has happened. First, the generator parameters of air-gap magnetomotive force, air-gap magnetic permeability and magnetic flux density on the fault are calculated, and the frequency characteristic of imbalance pull acting on rotor and that of pulsating magnetic pull acting on stator core are analyzed, then the rotor and stator radial vibration characteristics are gotten, which are that rotor vibration of fundamental frequency will increase, and stator vibration of second power frequency will decrease for one pair of poles generator. Next, the electric characteristic is analyzed, which is that the second harmonics circulating current between the stator winding parallel branches will increase when the fault occurs. Synthetically considering the vibration and circulating current characteristics, a method of the rotor winding inter-turn short circuit fault diagnosis, based on compositive characteristics of generator vibration and stator current, is developed. Finally, the vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

Through calculating the generator parameters of air-gap magnetomotive force, magnetic permeability, magnetic flux density, stator winding parallel-connected branches electromotive force distribution, the characteristics of the stator winding parallel-connected branches circulating current are analyzed. The results discover that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the stator winding inter-turn short circuit fault or the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault Considering the differences of the circulating current characteristics caused by different generator faults, a method of generator fault diagnosis, based on the stator winding parallel-connected branches circulating current characteristics, is developed. Finally, the circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above.

This paper emphasizes to develop a hybrid detection scheme for induction motor broken rotor bar fault, taking into account the intrinsic asymmetry, air-gap eccentricity and rotor misalignment of induction motors. Firstly, numerical simulation and related experiments of broken rotor bar fault have been performed successfully. Secondly, a series of principles and methods, which assure the sensitivity and reliability of broken rotor bar fault detection in practice, are generalized and revealed, based on thorough analysis of simulation and experimental results. Finally, a hybrid scheme to detect broken rotor bar fault, which blends continuous subdivision Fourier transform, self-adaptive filter, rotor slot harmonics based slip estimation and detection threshold self-tuning technique perfectly, is proposed in this paper. Fault detection instances in laboratory demonstrate that the presented scheme is valid and effective.

Generator rotor and stator vibration characteristics on stator winding inter-turn short circuit fault are analyzed. Through calculating the generator parameters of air-gap magnetomotive force, air-gap magnetic field energy and magnetic flux density on the fault, the frequency characteristic of imbalance magnetic pull acting on rotor and that of pulsating magnetic pull acting on stator core are found out. Then the rotor and stator radial vibration characteristics are gotten. Finally practically acquired vibration data on the spot of SDF-9 and MJF-30-6 type generator respectively, the results of verification show that the analysis is correct. On the other hand finds out the relationship between electric fault such as winding fault and mechanical vibration, and points out the vibration signal can be the symptom of winding faults as well as electric signal, and provides the new idea and method for study the electric fault

Stator and rotor vibration characteristics of generator are analyzed when the rotor winding inter-turn short circuit fault and the imbalance fault occur. The rotor vibration of fundamental frequency increases and the stator vibration of second frequency decreases when the rotor winding inter-turn short circuit fault occurs. But when the imbalance fault occurs, the rotor vibration of fundamental frequency increases and the stator vibration of second frequency increases too, so the stator vibration characteristics are different from that of the rotor winding inter-turn short circuit fault. Considering the differences of the stator vibration, a new diagnosis method of rotor fault, based on stator and rotor vibration characteristics, is developed. Comparing to the traditional method that only considering the rotor vibration signals, the rotor winding inter-turn short circuit fault and imbalance fault can be effectively diagnosed. Finally, the vibration data of a type of SDF-9 generator are measured in the laboratory to verify the theoretical analysis presented above

The stator-rotor-hybrid fault in squirrel cage induction motors, which means that rotor bar breaking fault and stator winding inter-turn short circuit fault occur simultaneously, has been investigated based on the motor multi-loop model. The results indicate that the features of rotor bar breaking fault and stator winding inter-turn short circuit fault always interlace and interact to some extent. The detection method, which is only suitable for single fault, may lead to a misinterpretation. In this paper, the stator-rotor-hybrid fault feature of rotor bar breaking and stator winding inter-turn short circuit has been summarized and the mutual relationship of the two types of fault has been disclosed by thoroughly analyzing the simulation and experiment results. As establishes an important theoretical foundation for joint detection of rotor bar breaking and stator winding inter-turn short circuit fault

This paper develops a sensitive and reliable detection scheme for broken rotor bar fault in induction motors, taking into account the intrinsic asymmetry, air-gap eccentricity and rotor misalignment. Firstly, numerical simulation along with related experiments of broken rotor bar fault are performed successfully. Secondly, by thoroughly analyzing the simulation and experiment results, a series of interesting highlights, which could help improve the sensitivity and reliability of broken rotor bar fault detection in actual field, are revealed explicitly. Finally, a novel scheme to detect broken rotor bar fault, which perfectly blends continuous subdivision Fourier transform, self-adaptive filter, rotor slot harmonics based slip estimation and detection threshold self-tuning technique together, and thus possesses high-sensitivity and high-reliability, is proposed in this paper. Fault detection instances in laboratory demonstrate that the presented scheme is valid and effective.

The radial basis function network (RBFN) is one of artificial neural networks (ANNs) applied widely. A new adaptive RBFN algorithm, named the two level iteration cluster algorithm, is put forward, which can calculate automatically RBFN parameters with samples, and overcomes the conventional algorithm's shortcoming where the hidden layer neuron number must be given in advance. In addition, a new generator vibration fault diagnosis method based on a stator and rotor vibration spectrum eigenvector is presented. Using practically acquired MJF-30-6 generator vibration data in three conditions of normal operation, rotor excitation winding short circuit and stator winding fault, the results of verification show that the method has higher diagnosis precision than the conventional method based on rotor vibration spectrum eigenvector.

This paper analyzes generator stator vibration frequency spectrum characteristic and correlation dimension characteristic based on phase space reconstruction of fractal theory, when generator is in three conditions of normal operation, rotor excitation winding short circuit and stator winding fault. The results show that rotor excitation winding short circuit and stator winding fault resemble stator vibration frequency spectrum, but three conditions have a different correlation dimension. So a new method of generator vibration fault diagnosis based on correlation dimension and artificial neural network (ANN) is proposed, which selects the stator vibration correlation dimension for the input vector of ANN, and practically acquired MJF-30-6 generator data for learning samples. The results of verification show that the method can identify efficiently three generator conditions.

The stator winding inter-turn short and rotor bar breaking are both frequent faults in squirrel cage induction motors. The previous work is inclined to detect one single fault, in other words, to detect the stator winding inter-turn short circuit or rotor bar breaking fault, separately. Hence there exists the misdetection probability due to the inter-influence of them. To solve that problem, this paper addresses the joint detection of the two faults. Firstly, this paper completes the numerical simulation by utilizing the multi-loop mathematical model. Secondly, some creative and interesting conclusions, which depict explicitly the inter-influence of the stator winding inter-turn short and rotor bar breaking faults, have been drawn based on the thorough analysis of the simulation results. Finally, a series of tests verify the necessity and effectiveness of the joint detection, which reduces the misdetection probability to a great extent. Further work will focus on refining the joint detection and applying it to the industrial site.

Based on the fault characteristics, where the exciting current increases and the output reactive power reduces, when an inter turn short-circuit occurs in rotor windings, and considering the saturated situation of generator, a fault characteristic mathematical model of inter turn short-circuits on generator rotor windings is founded. The method is verified by using the practical data.

On analyzing the influence of rotor slip influence potential on exciting current as asynchronous operation of asynchronous synchronous generator, the relation of static state stability limit with slip is clarified. Thereby the law of static state stability of asynchronous synchronous generator at any rotation rate is revealed in this paper.