Research On Alter Current Excitation Generator's Protection

With the rapid development of power industry, it is a tendency for electric energy to be transmitted in long distance, large capacity and high voltage level, which makes the problems of reactive power adjustment, static and transient stability of power systems more and more complex.Alter current excitation generators (ACEG) and traditional synchronous generator have different exciting structures and different excitation control strategy. ACEG has the advantages as the following: active, reactive, and the speed (in the exchange of excitation) can regulate independently; can not lose stabilization when absorbing mass reactive power ; be achieved variable speed constant frequency power. So ACEG has a wonderful applications and prospect in power industry and AC-electric transmission system. And its commercial application and protection studying are essential under the situation.This paper has proposed an AC-excited generator's complete protection scheme by analyzing the difference and the similarity of structure between traditional synchronous generator and ACEG. Analysis by that, the stator's structure of ACEG. Stator and traditional synchronous generator is exactly same ,and the fault feature of earth fault is same also,so ACEG.'s stator earth fault can use traditional synchronous generator's 100% stator earth fault protection. ACEG.'s inter short circuit can also use longitudinal differential protection by ratio braking style and transverse differential protection.The structure of AC excitation generators and synchronous generator rotor windings is totally different. According to AC excitation characteristics of the generator rotor windings, this paper presents a DC power supply plus scheme for the rotor windings point grounding protection,through theoretical analysis and simulation experiments, this method do not affect the normal operation of the rotor when the rotor windings is point grounding .The sensitivity of the way is high and doesn't change with the fault location. According to rotor windings fault (interturn short circuit, two ground), this paper presents a side of the stator current frequency of (1 ? 2s)f1 current and the ratio of positive sequence as the rotor windings failure criterion.A large number of theoretical analysis and simulation results show that this method can be very good at rotor winding fault detection , the sensitivity can meet the requirements, and not misoperation unde various fault conditions of the stator.