Wang Xiangheng

An equivalent instantaneous inductance-based technique for discrimination between inrush current and internal faults in power transformers

A novel equivalent instantaneous inductance (EII)-based scheme is proposed to distinguish the inrush current from internal faults in power transformers, which is derived from the inherent difference of the magnetic permeability, due to the saturation and unsaturation, in the transformer iron core between the inrush current and an internal fault. First, the EII that represents these differences is defined, and its calculation methods and the criteria to identify the internal fault in the time and frequency domains are respectively developed. A total of 98 experimental cases are used to test the performance of the technique. In all of the tests, the inrush current is characterized by the drastic variation of the EII, but the EII of the faulty phase is kept almost constant. The experimental results verify the dependability, security, and fast operation of the proposed scheme. Besides, its easy implementation in real time is another advantage of the proposed method because of its simplicity.

Nonlinear internal-model control for switched reluctance drives

A nonlinear internal-model control (IMC) based on suitable commutation strategy for switched reluctance motors (SRMs) is proposed. In the commutation strategy, a fixed critical rotor position is defined as the commutation point, which results in reduced computation. Combined the simplicity of the feedback linearization control and the robustness of IMC structure, the proposed drive has excellent dynamic and static performances for the torque and current control. The scheme is analyzed, and some important properties are obtained. Simulations and experiments were carried out on a 7.5 kW four-phase SRM, and the results show that the ripple of the output torque is very low in spite of model-plant mismatches.

A small single-phase switched reluctance generator for wind power generation

This paper discusses an 8/8 configuration single-phase switched reluctance generator (SRG), which is applied for wind power generation. It describes the current-chopping control (CCC) method of generating and the speed feedback control method of the whole system. The hardware implementations and some of experimental results are represented.

Steady-state performance of synchronous generators with AC and DC stator connections considering saturation

Synchronous generators with ac and dc stator connections are widely used in systems where simultaneous ac and dc power supplies are needed. For these systems the voltage harmonic distortion of ac voltage, dc voltage ripple, and dc voltage varying range are of special interest. Because of the commutation of rectifier and the saturation of magnetic circuit, the accurate calculation of voltage harmonic distortion and dc voltage varying range is comparatively difficult. This paper describes a mathematical model on the basis of the multiloop method and FEM, which aims at calculating the steady-state characteristics and the voltage waveforms of ac winding accurately. With this method, the full synergic effects of space harmonics resulting from the magnetic circuit geometry, saliency, saturation, winding layouts, and slotting are included. The calculated results are compared with those of experiments.

Research on internal faults of generators and their protection schemes in Three Gorges hydro power station

Based on the multi loop method, the internal faults of generators in Chinas Three Gorges hydroelectric power station, including the interturn short circuit in the same branch, the short circuit of two branches of same phase and the short circuit of two branches of different phases are calculated. According to the calculated data of 60 short circuits of 2 generators, protection schemes are presented. Single element transverse protection is more the attractive scheme owing to its high sensitivity and simplicity. The high sensitivity single element transverse differential, noncomplete or complete longitudinal differential protections constitute multiple protection functions.

Research on the internal faults of the salient-pole synchronous machine

Adopting the multi-loop method, the mathematical model of the salient-pole synchronous machine is established in which the internal faults can be taken into account. Based on the model, a simulation program of the internal faults is made. It is found that the simulation results are consistent with the experimental data under the same condition, which verifies the mathematical model. According to the simulation results, the variational regularities of transient and steady-state currents are discussed. Referring to a few protective schemes against the internal faults, the protective sensitivities are calculated. Then the sensitivity based on the steady-state fundamental component and that based on the transient fundamental component are compared.

NEW DEVELOPMENT OF TORQUE ANALYSIS OF SYNCHRONOUS MACHINE

ABSTRACT By using a multi-loop model, a new technique for analysing the torque of a synchronous machine is presented in this paper. The electro-magnetic torque of the machine which is very difficult to calculate in some operation conditions by other methods, can be obtained from the inductances of the machine and the currents of every loop of the machine, then the average torque and the pulse torque by Fast Fourier Technique. Comparing the results obtained by the new technique with an established method, the new method is justified.

A study of armature winding internal faults and protection schemes for turbogenerators

The internal fault of an armature winding is one of the most severe faults for turbogenerators. It is necessary to know the transient values of the machine when the internal faults occur so as to design suitable protection. Based on the multi-loop method, a mathematical model of the turbogenerator with an internal fault is developed. The air-gap permeance analysis method is used to calculate the parameters and the eddy current of the solid rotor. The method is verified by computer simulation and experimental results. The developed model provides a theoretic basis for predicting transients and developing protection schemes for turbogenerators with internal armature faults.

Comprehensive simulation for faults in the stator windings of salient-pole synchronous generators

Based on the multi-loop circuit method of calculating the inductance parameters of AC machine windings, a comprehensive and transient simulation model is established for various faults in the stator windings of a salient-pole synchronous generator. In term of different fault styles, the fault-associated matrix in the state equations is modified, and all of faults in stator windings including internal faults and ground faults can be simulated in this unified model. Simulation results are compared with those of experiments to verify the proposed method. Using the model to study the variation of current and voltage is conductive to analyze the features of faults, and design the relevant protection scheme.

Simulation and operational protection of three-phase/twelve-phase hybrid AC-DC supply generator system

The hybrid AC-DC supply has been applied to various situations. It provides simultaneous AC and DC power with least weight, volume and cost to meet the special requirement of mobile power networks. In this paper, a mathematical model, based on the multiloop method, including speed regulator and excitation regulator, is established to reflect the system operation aspect. The simulation results of voltage harmonics are compared with experiments to verify the validity of the mathematical model. The DC side power oscillation and short circuit may result in system breakdown. The simulation program provides the guideline for system operation and protection. The simulation results showed the factors that affect the amplitude and frequency of the DC side power oscillation. The q-axis winding and feedback control of the DC load current on the excitation voltage can increase system stability. The DC side short circuit currents are also calculated for the tuning of the relays.