Xu Guorui

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.

Time Step Finite Element analysis for synchronous generator's asynchronous operation during loss of field

In order to study synchronous generators asynchronous operation during loss of field, the Field-Circuit Coupled Time-Stepping Finite Element Model (T-S FEM) is built, in which the saturation of magnetic circuit, magnetic distortion, and harmonic field and so on are considered. The simulation modeling is verified by testing. The physical process of the synchronous generators asynchronous operation during loss of field is analyzed. On that basis, take a single-machine infinite-bus for example, two conditions of the synchronous generators asynchronous operation during loss of field are simulated, one of which is excitation opened circuit, and the other is excitation shorted circuit. The difference under excitation opened circuit between T-S FEM and PSD-BPA simulation is bigger than excitation shorted circuit.

Loss and Air-gap Force Analysis of Cage Induction Motors With Non-skewed Asymmetrical Rotor Bars Based on FEM

Non-skewed asymmetrical rotors bars can be used to eliminate the slot harmonic fields and the resulting noise and vibration in cage induction motors. However, it is difficult to determine the spatial distribution of the asymmetrical rotor bars and the slot combinations, which can affect the loss and the air gap force significantly. With a 5.5 kW, 4-pole induction motor as an example, this paper studies the influence of the above factors on the loss and the air gap force by time-stepping finite element method, and the experiments are performed to validate the calculations.

Piecewise variable parameter loss model of laminated steel and its application in fine analysis of iron loss of inverter-fed induction motors

Due to the coaction of supply harmonics and harmonic fields inside the motors, the mechanism and distribution characteristics of iron losses become more complicated in inverter-fed induction motors. Therefore, accurate prediction and fine analysis of iron loss are very important at the design stage of high-efficiency inverter-fed induction motor. In order to predict the iron losses accurately, this paper proposes a piecewise iron loss model whose parameters vary with the amplitude and frequency of flux density, and two additional flux density terms are introduced to the classical iron loss model considering the nonlinearity of magnetic material and harmonic fields. With this model, the iron losses are calculated for an inverter-fed 5.5kW induction motor. The results reveal the distribution characteristics of hysteresis and eddy current losses in stator and rotor cores, and acquire the characteristics of additional iron loss caused by harmonic fields. By the comparison of predicted and measured no-load iron loss under different supply voltages and switching frequencies, the proposed model and analysis results are validated.

The influence of rotor slot wedge material and conductivity on first swing stability of turbine generator

The turbine generator rotor damping system consists of damping bars, iron core and slot wedges. The rotor slot wedges are not only preventing the field windings out of slot, but also provide the damping effect to keep power system stability. Since there are several materials to choose from and their conductivity is different, it is necessary to study the influence of rotor slot wedge material on First Swing Stability (FSS). In this paper, we establish the Field-circuit-network coupled time-stepping finite element model, which is verified by the experiment of model machine. With a 300MW turbine generator as an example, the FSS limits of turbine generator with rotor slot wedge made from aluminum, copper base bronze and stainless steel are calculated and compared; the key factor affecting the FSS limit is obtained. In order to find the optimal material for FSS improvement, the FSS limits are calculated with the conductivity of rotor slot wedge in the range of 0 to aal (conductivity of aluminum). The result shows that the FSS limit of turbine generator with the rotor slot wedge made from stainless steel is larger than that made from aluminum and copper base alloy. The variation law of FSS limit with the change of rotor slot wedge conductivity is revealed. The results provide important reference for improving the FSS in the design of turbine generator.

Practical model for energy consumption analysis of beam pumping motor systems and its energy saving applications

Due to the dynamic load and the complex mechanical link, it is difficult to precisely analyze the characteristics of the energy consumption of Beam Pumping Motor Systems (BPMSs), in the development of energy saving approaches in oil production systems. To solve this problem, this paper establishes a practical model that combines the standard differential equation of induction motor, the crank movement equation and the wave equation of sucker rod, the loss equations of the low- and high-voltage supply lines and distribution transformers, for energy consumption analysis of BPMSs. With this practical model, the influence of different factors, including the load fluctuation, balance degree and dynamic liquid levels, on the electrical loss characteristics of BPMSs, can be analyzed. The variation of the electrical loss in a Type 12 BPMS driven by a 37kW induction motor with the different dynamic liquid levels and the balance degrees is studied, and the distribution characteristic of each loss component under five typical load conditions in oil field is also analyzed. It is revealed that the proportion of iron loss is about 40% of the total electrical loss. The correctness of the model is verified by comparing the calculated results with the measured data for a standard oil well. In addition, the energy saving devices based on the theoretical results obtained by the presented model achieve a significant energy saving ratio in the practical application at oil fields.

Piecewise Variable Parameter Piecewise Variable Loss Model of Laminated Steel and its Application in Fine Analysis of Analysis of Iron loss of Inverter-Fed Induction Motors

Due to the coaction of supply harmonics and the harmonics resulting from the motor structures, the mechanism and distribution characteristics of iron losses become more complicated in inverter-fed induction motors. Therefore, accurate prediction and fine analysis of iron loss are very important at the design stage of high-efficiency inverter-fed induction motors. In order to predict the iron losses accurately, this paper proposes a piecewise iron loss model whose parameters vary with the magnitude and frequency of flux density, and two additional flux density terms are introduced to the classical iron loss model considering the nonlinearity of magnetic material and harmonic fields. With this model, the iron losses are calculated for an inverter-fed 5.5 kW induction motor. The results reveal the distribution characteristics of hysteresis and eddy current losses in stator and rotor cores, and the characteristics of additional iron loss caused by harmonic fields. By the comparison of predicted and measured no-load iron loss under different supply voltages and switching frequencies, the proposed model and the analysis results are validated.

Loss and air-gap force analysis of cage induction motors with non-skewed asymmetrical rotor bars based on FEM

Non-skewed rotors can be used to eliminate the slot harmonic field, as well as, the noise and vibration can also be weakened effectively. However, it is difficult to determine the spatial distribution of the asymmetrical rotor bars and slot combinations, which can affect the loss and air-gap force significantly. Taking a 5.5kW, 4-pole induction motor as an example, this paper studies the influence of the above factors on the loss and air-gap force systematically, by using Finite Element Method (FEM), and the experiment validation on efficiency and no-load noise are also performed on a 5.5 kW prototype.

Separation of slip- and high-frequency electromagnetic quantity and its application in rotor loss fine analysis of induction motor

Due to coupled slip- and high-frequency electromagnetic quantity with load conditions, it is difficult to separate the additional iron and copper losses caused by the harmonic field accurately at rotor side of induction motor within a power cycle. To solve this problem, this paper proposes a separation method of rotor electromagnetic quantity with the slip frequency. In this method, the amplitude of flux density or current density with slip-frequency can be solved by Discrete Fourier Transform (DFT) on a spatial field distribution at a random moment, and the polynomial combined high-frequency sine functions are adopted to fit the curves in a power cycle by Least Square Method (LSM); finally, the loss caused by different harmonic fields can be calculated separately and accurately. The correctness of the proposed method is verified by comparing with the computed flux density with a slip cycle, and its application on rotor losses fine analysis is also presented.

The influence of rotor damping system of turbine generator on small disturbance characteristic

In this paper, we study the influence of rotor damping system on small disturbance characteristic of turbine generator connected to power system. Considering the complex rotor damping structure of turbine generator, we establish Field-circuit Coupled Time-Step Finite Element Model and test this model by the experiment of 7.5 kW model machine. Based on this model, we take a 300 MW turbine generator as an example to study the influence of damping bar, rotor iron core and conductive slot wedge on small disturbance characteristic. We investigate the importance of the rotor damping system to small disturbance characteristic and find its impact is not negligible. By comparing the small disturbance characteristic indexes affected by three components of rotor damping system respectively, we conclude that the rotor slot wedge plays a leading role in small disturbance characteristic.