Analysis Of Characteristics For 1000MW Hydro-generator Under Loss Of Excitation

Due to the wide distribution of rivers and rich water resources in our country, the development of hydro-generator improves energy production and provides protection for the rapid economic development. Because of the serious consequences produced by frequent loss of excitation failures for huge hydro-generator, the importance of researching on loss of excitation failure for 1000MW hydro-generator is propounded in this paper. The performances for 1000MW hydro-generator under loss of excitation are studied, including the variations of electrical quantities of stator and rotor in the process of loss of excitation, change of electromagnetic field under steady state asynchronous operating after loss of excitation, and components of air gap flux density.First of all, the process from loss of excitation, critical out of synchronism to steady state asynchronous operation is expounded in this paper. The forming principle of pulsating magnetic field of rotor, and the influences of electrical quantities after failures are analysed. Furthermore, through the decomposition of asynchronous torque, the root reasons why generator set oscillates after loss of excitation failure are mastered.Sencondly, mathematical model of 1000MW hydro-generator is established, and on this basis simulation model of one machine-infinity bus system is also established. Then under different input power, the loss of excitation failures, such as direct short-circuit, open-circuit of excitation windings and short-circuit with de-excitation resistance, are simulated. After simulation, variations of stator voltage, stator current, reactive power and power angle are given, and reasons for changes of paraments and consequences produced by loss of excitation are analyzed. Meanwhile, after simulations of oscillation and short-circuit fault, variations of the same paraments are obtained and compared with the results of loss of excitation, and then the essential differences are summarized. Finally, according to the dimensional data of 1000MW hydro-generator, a two-dimension physical model is established. In order to simulate different kinds of loss of excitation failures, excitation windings are setted as external circuit and controlled by switch. Based on the model, the magnetic field distributions and air gap flux density compositions for asynchronous operation of hydro-generator during loss of excitaion are calculated on rated and different input power conditions. By comparing the simulation results, variation of harmonic component amplitude is given, and the reasons for the decrease of air gap flux density distortion are analyzed.