Patent ID: 6420876
Filing Date: 2002-07-16
Classification: G01R

Abstract:
A method for location of a fault which has occurred on one of a plurality of lines in a medium-voltage (MV) network where the lines extend from the switchgear located in an MV station and where the location of the fault is determined with the aid of measured values of the common supply voltage of the lines and the sum current of the lines in the station prior to and after the occurrence of the fault, and using data representing the configuration of the network and electrical data including the number of lines, branches, lengths of lines between the branches and the representative line impedances and of actual loads on the lines and loads at branches, and wherein knowledge is obtained, via a superordinate protection system, as to which line has become faulty and which fault has occurred, wherein a fictitious positive-sequence impedance for the line as viewed from the ith branch is determined as follows: Z_i+1=ZLi&af;(Zi-ZSi)ZLi-(Zi-ZSi)(29)whereZLi is equal to the load impedance at the ith branch, Z1 is equal to the fictitious positive-sequence impedance of the line as viewed from the iâˆ’1th branch, ZSi is equal to the impedance of the ith line section, and the determination is stated by assuming Zi=Z0,where Z0 is equal to the positive-sequence impedance of the line, as viewed from the station, and is determined with the aid of voltage and sum current values, measured at the station, said network data, and the determination of the fictitious positive-sequence impedance of the line, as viewed from the ith branch, is repeated until two consecutive values Zi Ziâˆ’1 change from a positive value to a negative value, whereupon the distance to the fault from the ith branch is determined to be: lf=Im&af;(Zi)Im&af;(ZSi)&it;li(30)whereIm(Zi) is equal to the imaginary part of Zi, Im(ZSi) is equal to the imaginary part of ZSi, li is equal to the length of the ith line section, and the distance from the station to the fault is equal to the sum of the lengths of all line sections up to the ith branch plus the calculated distance li to the fault from the ith branchlF=&Sgr;li+lf,â€ƒâ€ƒ(31).