Theoretical Analysis And Online Monitoring Of The Interturn Short Circuits Of Field Windings In Multiphase Annular Brushless Exciter At Nuclear Power Plant

As a special type of generator,multiphase annular brushless exciter is widely used in nuclear power plant in order to supply high-quality excitation source.In the case of internal faults which frequently occurred in the brushless exciter,the exciter's "weak protection" state can not meet the requirements of the unit's safe and stable operation.In order to realize the online monitoring of ISCFW by electric quantities in operation,this dissertation conducts research on the mathematical model establishment,the comparison between the experimental and simulation results,fault criterion and its mechanism,online fault monitoring principle and fault protection device.Based on multi-loop analysis method,a general mathematical modeling method of multiphase annular brushless excitation system with ISCFW is established.We take a single coil as the basic unit,constructing the inductance parameter matrix among the components.According to the circuit components,we consider the actual connection and establish the system of equations of multiphase annular brushless exciter.According to the “on” or “off” state of the diodes,update the basic loop matrix in real time,Completing the final iteration solution.In order to verify the correctness of the mathematical modeling methodology,this paper firstly establish the mathematical model of the 11-phase model machine based on its parameters,and calculate the inductance parameters between rotor and stator.The experiment research has been done in the model machine,and waveforms of related electrical quantities have been compared.The experimental and simulation waveforms of the model machine are are identical with each other,which verifies the correctness of the general modeling method.This paper summarizes the errors' causes and discusses the ways to improve the accuracy of the mathematical model.In order to find out the harmonic characteristics of postfault stator and rotor current,a general mechanism analysis method for ISCFW of the brushless exciter is proposed.Taking the general m-phase P-pole-pair brushless exciter as the research object,the characteristics of steady-state fault of stator and rotor currents were theoretically analyzed based on the magnetic field produced by stator and rotor windings and their mutual induction when the fault occurs.It can be concluded that m/P times harmonics are in the field current while all harmonics are in the armature current.The simulation research of the multiphase annular brushless exciter further verifies the correctness of the mechanism analysis.As an extension of the above mechanism analysis,we analyze the common armature windings types of the general generator based on the structure research of different types of generators.We analyze the influence of the armature windings types on the harmonic characteristics of the postfault steady-state field current,and improve the general theoretical analysis method of ISCFW of general generator.This paper compares the fault characteristics of different internal faults occurred in exciter and clarifies the fault characteristic uniqueness of ISCFW.Based on the change regulation of the stator field current,we formulate the corresponding the online principle of ISCFW,and customize the value set.According to the aforementioned protection monitoring principle,we develop the protection device,and test the performance of the device on the model machine.The experimental results verify the effectiveness of the monitoring principle and the correctiveness of the electric quantity acquisition,the electric quantity calculation and the fault judgment.