| System commissioning is the key link to ensure the smooth operation of the UHV AC project,which undertakes a comprehensive test of the performance of the primary and secondary equipment of the project,and a comprehensive inspection of the operating characteristics of the system.Meanwhile,system commissioning bears the heavy responsibility of providing technical basis for project acceptance and operation.In order to ensure that the commissioning test scheme is reasonable and feasible,a system commissioning research is carried out according to the actual characteristics of the project and the needs of the test assessment.Among them,the research of overvoltage and electromagnetic transients is one of the important topics.It is necessary to predict the overvoltage and overcurrent phenomena that may occur during the test,analyze the safety measures that should be taken during the test,and formulate relevant accident plans and preventive measures.On this basis,compile a reasonable system commissioning program and specific test items.To this end,the dissertation studies the generation mechanism,regular characteristics and suppression measures of core electromagnetic transient problems faced by the UHV AC transmission engineering system debugging.The main research work is as follows:Firstly,it summarizes the system commissioning of UHV AC engineering system,enumerates the UHV lines that have been put into operation in our country,and subdivides the division of labor of each test group during the test.The facilities and site of the system commission test are demonstrated,and the principles and classification of the commission are clarified.The five kinds of tests involved in the system commissioning process are described,including switching 1000 k V no-load line test,switching 1000 k V no-load transformer test,switching 110 k V side low-voltage reactor and capacitor test,1000 k V closed loop test and artificial single phase grounding test.Presenting the purpose of the test,and explaining the specific steps of various tests under actual engineering.Secondly,the electromagnetic transient problems of UHV AC engineering system commissioning are divided into two categories for research.First,analyzing the electromagnetic transient problems caused by the switching test of the main equipment,including the overvoltage of the no-load line closing operation,the overvoltage and the magnetizing rush current of the no-load transformer and the switching over voltage of low voltage reactor and capacitor.The mechanism and restraining measures of various electromagnetic transient problems are analyzed.Based on the actual parameters of the Shandong ring network project,building a calculation model to simulate the electromagnetic transient problems under various test operations.during the test,calculating the over-voltage and over-current amplitudes of the main equipment,and verifying the suppression effect of the control measures.Evaluating the operating conditions of the equipment in combination with the technical conditions,and proposing the corresponding safety measures.The simulation results are compared with the measured values of the system commissioning test to verify the authenticity and accuracy of the simulation calculation.Finally,it is predicted that there may be other electromagnetic transient problems during system commissioning,including induced voltage and induced current,power frequency overvoltage,secondary arc current and recovery voltage,and non-full-phase operating overvoltage.Carrying out the formula derivation and theoretical analysis of each electromagnetic transient problem,and analyzing the suppression measures such as the installation of parallel reactors on the line and the addition of small reactances at the neutral point of the parallel reactor.As a result,the power frequency overvoltage is too high,and the addition of a small reactance at the neutral point has a significant effect on the suppression of the secondary arc current and recovery voltage.Various overvoltage amplitudes can meet the requirements of UHV projects. |
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