Symmetrical Loss of Excitation Fault Diagnosis in an Asynchronized High-Voltage Generator

Abstract

As a new type of generator, an asynchronized high-voltage generator has the characteristics of an asynchronous generator and high voltage generator. The effect of the loss of an excitation fault for an asynchronized high-voltage generator and its fault diagnosis technique are still in the research stage. Firstly, a finite element model of the asynchronized high-voltage generator considering the field-circuit-movement coupling is established. Secondly, the three phase short-circuit loss of excitation fault, three phase open-circuit loss of excitation fault, and three phase short-circuit fault on the stator side are analyzed by the simulation method that is applied abroad at present. The fault phenomenon under the stator three phase short-circuit fault is similar to that under the three phase short-circuit loss of excitation. Then, a symmetrical loss of the excitation fault diagnosis system based on wavelet packet analysis and the Back Propagation neural network (BP neural network) is established. At last, we confirm that this system can eliminate the interference of the stator three phase short-circuit fault, accurately diagnose the symmetrical loss of the excitation fault, and judge the type of symmetrical loss of the excitation fault. It saves time to find the fault cause and improves the stability of system operation.Energies 2018, 11, 3054 2 of 18 power, and speed can be adjusted independently; power generation with variable-speed and constant-frequency; deep lead phase operation is also possible [2]. Numerous studies have been conducted to study the static stability of asynchronized synchronous generators [3,4] and the operation action for asynchronized turbogenerators with excitation disappearance [5].In the past decade, the research on the loss of excitation faults for the Powerformer have shown that the Powerformer can enter a stable asynchronous operation state within a short period of time [6], and its stator current will increase to 1.2~1.5 times after a loss of excitation [7]. This research group used the modulus maximum detection method of wavelet transform to analyze the electrical quantity signal during the loss of excitation fault and determined the loss of excitation protection scheme for the Powerformer. The protection scheme can effectively prevent the misoperation of the protection device when the system is under a short-circuit fault and oscillation [8]. If we focus on the changes of electrical quantities after a loss of excitation for asynchronized high-voltage generators and adopt an effective loss of excitation fault diagnosis technique, the loss of excitation fault can be accurately determined and remedied in time to ensure the safe and stable operation of the power system. Therefore, it is extremely necessary to investigate the fault diagnosis for asynchronized high-voltage generators.Numerous studies have been done to diagnose the loss of the excitation fault of the generator by measuring the rotor signals [9] and the changes in resistance and reactance [10,11]. The main shortcoming of t...

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