| The AC 380 V low-voltage system in the main building of Huadian Suzhou power generation company mainly supplies power to the key auxiliary equipment such as the lubricating oil system,sealing oil system,steam turbine condenser vacuum system,boiler fire detection cooling system,etc.once the power is cut off,the normal operation of the generator will be affected.In order to improve the reliability of power supply,the neutral point of the system is grounded by small current through 44 Ωresistance.However,after the grounding line selection system is put into operation,the accuracy of line selection is not ideal.For this reason,the author based on his own job,combined with the second phase transformation project,studied the new grounding line selection principle,and applied it in engineering.The main work and achievements of this paper are as follows:Firstly,several voltage levels and corresponding neutral grounding modes in the power plant are discussed.The neutral grounding mode of low-voltage 380 V system through 44 Ω high resistance and small current is emphatically analyzed.The problems of low recognition rate and poor system integration in the initial installation of small current grounding line selection system are summarized.Secondly,wavelet transform is used to analyze the steady-state and transient fault signals when single-phase grounding occurs in small current grounding system.PSCAD power system simulation software is used to simulate the process that the amplitude ratio of zero sequence current between non fault line and fault line decreases gradually when the single-phase grounding resistance increases from 0 Ω to500 Ω.Then,a method of small current grounding line selection based on Wavelet and correlation coefficient is proposed.The method is tested by simulation and artificial single-phase grounding fault.The results show that the theoretical accuracy of the method can reach 100%.Thirdly,this paper mainly expounds the small current grounding line selection device after the transformation and upgrading of line selection principle from the perspective of hardware.In view of the isolated operation of each line selection unit,from the perspective of economy and convenience,this paper puts forward the networking integration scheme of grounding line selection device based on mobile phone cloud platform intelligent mobile terminal app.Finally,the operation effect of the upgraded small current grounding fault line selection system is compared and evaluated,and some typical single-phase grounding fault line selection cases are selected for detailed analysis and cause tracing.The data statistics of the preliminary application of the system show that the accuracy of line selection can reach 99%.This study has important reference value for the performance improvement of grounding line selection system of AC 380 V low voltage system in the main plant of Huadian Suzhou power generation company,as well as the later networking and information integration. |
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