Diagnosis And Prevention For Low Voltage Reactor Of Extra High Voltage(EHV) Substation

Low-voltage reactor is one of the most important electrical equipments in EHV substations,which can generally be divided into two kinds,the series reactor and the parallel reactor.The series reactor works with the capacitor bank in series to suppress the high harmonics and limit the closing inrush current as well as prevent harmonics from damaging the capacitor.The parallel reactor is generally used to compensate for reactive power,regulate and stabilize the grid voltage,ensure the safe operation of the power system,reduce loss,improve the voltage quality and power supply efficiency.With the increase of electrical load,the rapid expansion of extra-high voltage power grids and the development of automatic control technologies such as AVC,the number of low-voltage reactor has increased dramatically.However,a large amount of data and actual operation cases indicate that dry-type air-core reactors frequently suffer from frequent switching over-voltage,old equipment replacement,insulation aging,insulation cracking and other factors,resulting in frequent dry-type air-core reactor failures during operation.Various relevant problems seriously affect the safe operation of the power grid.Specially in recent years,a number of dry-type air-core reactor fire accidents have occurred in the Shandong electric power EHV grid,causing serious economic losses.Based on relevant literature as well as the operation and maintenance practices of low-voltage reactors in Shandong electric power grid,this thesis systematically analyzes the causes and characteristics of the failures of low-voltage reactor,outlines the methods of failure diagnosis of low-voltage reactor,and puts forward effective preventive measures according to common failures.The main research work is addressed as follows:(1)Analyze the types and causes of common failures of low-voltage reactors in EHV substations.First,the common types of failures are listed and elaborated in terms of some cases in recent years.Then,combined with concrete cases,causes of common failures are summarized and refined.(2)Research on the comprehensive failure diagnosis method of the low-voltage reactor in EHV substations.First of all,according to the types and causes of common failures,the common failure diagnosis methods are enumerated and analyzed in detail,including their own principles,roles,advantages and disadvantages.Furthermore,a comprehensive diagnostic method is presented,which is useful and effective in operation and maintenance practices of the power grid.Finally,taking the Shandong power grid EHV substation as example,the applications of the comprehensive diagnostic method are studied.(3)Present effective preventive measures for the common failures of the low-voltage reactors in EHV substations,aiming to eliminate potential safety hazards in the early stage and thereby prevent accidents.First,this thesis respectively analyzes the principles and implementation effects of various types of preventive measures,including strengthening the control of equipment access,strengthening operation and maintenance,and weakening closing surges and switching over-voltages.Then,the new technology of phase selection and closure in the low-voltage reactors is focused on.By means of the new technology,the over-voltage and closing surge of the low-voltage reactor circuit can be reduced,which means that the inter-turn insulation failure of the low-voltage reactor can be solved fundamentally.