Research On Protection And Fault Location Of Generator Stator Single-phase Earth Fault

Generator stator single-phase ground fault may burn the stator core,and even further develop into more serious fault.In addition,the iron core structure of generator is complex,it will cause huge economic losses if the stator core is damaged The dissertation takes generator stator single-phase ground fault as the research object,the following aspects phase selection,fault location,a dual frequency injection stator grounding protection and selective stator grounding protection are studied.The main work and innovations of this dissertation are as follows:The dissertation analyzes winding potential phase of large non-salient pole generator,and proposes two winding potential expression which considering the phase of winding potential.Compared with the traditional winding potential expression,the new expression which considering the phase of winding potential,provides the theoretical basis for studying the phase characteristics of electrical quantities when stator ground fault is occurred.A new phase selection method based on phase angle of zero sequence voltage is proposed,which improves the sensitivity of the phase selection algorithm for high resistance ground fault.The action area of the new phase selection algorithm is deflected clockwise,which can solve the problem of low sensitivity or mal-operate by using phase selection algorithm of low voltage.Theoretical analysis and simulation indicating that the new method is suitable for all kinds of neutral grounding modes,it also can be recognized reliably when there is a high impedance grounding fault.The correct fault selection provides the basis for the subsequent fault location of the stator single phase to ground fault.A method used to calculate the grounding resistance and realize the fault location for large salient pole generator is proposed base on zero sequence voltage phase characteristics.Accurately calculating transition resistance is the key to fault location for the stator ground fault.The dissertation finds the relationship between phase angle of zero sequence voltage and transition resistance,the transition resistance can be calculated by only using the fault signal of the generator.Simulation analysis and physical test are carried out,indicating that the method is suitable for large salient pole generator,the positioning results are accurate and can meet the engineering needs in all kinds of neutral point grounding mode.It is pointed out that the winding potential phase of the large non-salient pole generator will affect the accuracy of the fault location,so the phase characteristics of the winding potential must be considered when calculating the transition resistance by using the generator self fault signal.By considering the phase characteristics of the winding potential,fault location methods based on the characteristics of zero sequence voltage phase and phase voltage deviation are improved.The fault location methods are verified by simulation,indicating that the improved fault location methods which considering the phase characteristics are suitable for large non-salient pole generator,the positioning results are accurate and can also meet the requirements when the high resistance grounding fault occurs no matter which kinds of neutral grounding modes.A dual frequency injection stator grounding protection scheme is designed,the injection frequency are 20 Hz and 80 Hz.The protection scheme should be locked in the process of generator starting and stopping,which can protect the generator stator winding in the whole process.The frequency of the high frequency injection signal is the key to the protection.In this dissertation,the frequency of the high frequency injection signal is studied from the aspects of the sensitivity of the injection protection,the design of the filter parameters and et al,the high frequency is determined as 80 Hz.A new stator grounding protection for the expanded unit connection is proposed by using the characteristic of the admittance asymmetry degree.It solves the problem that the stator ground fault protection is not selective when used for generators in expanded unit connection.The admittance asymmetry of generator is analyzed when there is a stator grounding fault.For the fault generator,the admittance asymmetry parameter is "yes",its value is greater than 1,and the admittance asymmetry of the non fault generator is "no",its theoretical value is 0.The new protection scheme finds the fault generator by calculating the maximum of the admittance asymmetry,which can find the fault generator and has high sensitivity.The proposed method are simulated and tested,and the test results verify the feasibility of this method.