Research On Rotor Grounding Protection Method Based On Multiple Feature Quantities

One point rotor ground fault of a generator is a common problem that affects the safe operation of the generator.To ensure the stable operation of the generator,rotor ground protection is provided in the generator protection,but there are sometimes false alarms and missing alarms.Therefore,this paper proposes a rotor ground protection method based on multiple characteristic values,which aims to solve the problem of rotor ground protection maloperation and has important significance for ensuring the safe operation of generators.Firstly,this paper compares various existing rotor ground protection principles at home and abroad,analyzes and summarizes the advantages and disadvantages of each protection principle.Based on the protection characteristics and application prospects,the double-ended square wave injection rotor ground protection is selected as the main research object of this article.The Matlab/Simulink simulation models of rotor one-point grounding and rotor two-point grounding are established,and the influence of various parameters in the rotor ground protection circuit on the protection accuracy and the setting principles of the rotor ground protection are analyzed;Then,theoretical and simulation analyses are conducted for three types of faults that frequently cause field protection maloperation,and corresponding diagnostic algorithms are studied.Aiming at the problem of excitation voltage fluctuation,it is proposed to take into account the effective value of excitation voltage in the calculation of ground resistance,and recalculate the ground parameter value using the full resistance formula.A fault diagnosis algorithm based on real-time voltage detection and voltage waveform area threshold judgment is proposed for poor contact of carbon brushes.Aiming at the single-phase ground fault at the low voltage side of the excitation transformer,the time-domain characteristic parameters of the ground voltage are extracted,and the membership matrix is obtained using the FCM algorithm to identify the fault.Finally,fault diagnosis methods are integrated to form a logic algorithm for rotor ground protection based on multiple feature quantities.In order to verify the feasibility of this method,the hardware and software designs for data acquisition,data processing,protection logic algorithms,and waveform display functions were completed.The verification prototype selected STM32F407 to control AD7606 for data sampling,and the SBC870 industrial computer of Yingchuang Company paired with ESMARC3352 industrial control chip to complete data processing and waveform display.Subsequently,a test platform was built,fault simulation and ground protection experiments were conducted,and the test results were analyzed to prove the feasibility of rotor ground protection based on multiple characteristic quantities.In order to improve the reliability of the protection device and avoid the failure of the square wave injection rotor ground protection when the square wave power supply is abnormal,a dual protection algorithm soft redundancy design is proposed.By adding electronic switches and resistors to the protection circuit,the grounding parameters are calculated twice in a square wave cycle when the square wave power supply is normal.When the square wave power supply is abnormal,the rotor insulation to ground is judged through switching sampling and independent protection algorithms.Establish a simulation model to verify the switching and operation of the dual protection algorithm,and compare and analyze the detection and protection accuracy under normal and abnormal conditions.Propose solutions to the impact on ground capacitance in practical work.