Study On Internal Fault Location And Isolation In Medium Voltage Micro-grid Based On Integrated Protection

With the growing shortage of resources and more attention on theenvironmental issues, the technology of distributed generation is becoming one ofthe major research directions. The most efficient way to use distributed generationis in the form of micro-grid, which is connecting distributed generation into grid.Micro-grid could improve area power supply reliability and power quality of loadin the micro-grid. Meanwhile, the problems that bidirectional power flow inmicro-grid and tremendous difference of short circuit current in two modes ofoperation make the traditional protection methods invalid in two operate modes.Therefore, it is important to study relay protection of micro-grid theoretically andpracticably. Firstly, this paper introduces domestic and international research statusof micro-grid relay protection and integrated protection. When faults occur inmicro-grid in grid-connected operation, the method of changing protection settingvalue and installing directional elements to protect micro-grid is discussed based onthe fault characteristics of micro-grid. For the key research of micro-grid protectionin isolated island operation is aimed at internal faults, internal fault detection andisolation method based on integrated protection is discussed in this paper. Themodified algorithm of fault detection and isolation is adopted to realize fast faultlocation and clearing. The major work of the paper is as follows:(1)The fault characteristics of micro-grid when internal fault happens arestudied. The differences of internal short circuit current under grid-connectedoperation and islanding operation of micro-grid are presented. The fault currentcharacteristics are studied in detail when three-phase short circuits occur indifferent locations of micro-grid in islanding operation, and results are verifiedthrough simulations.(2)The impacts of micro source on protection of distribution network areanalyzed when micro-grid operates with grid. Then the method of changingprotection setting value and installing directional elements is discussed to protect micro-grid when internal faults happen.(3)The internal fault detection and isolation method based on integratedprotection theory is applied to detect and isolate faults accurately in micro-grid.The modified algorithm of fault detection and isolation is presented based on theoriginal matrix algorithm of fault location. The fault-tolerant performance of themodified algorithm is studied for abnormal situations as fault information distortsor misses.