| 摘要 |
The invention object relates to electrical networks with dead earthed neutrals, in particular to distant protection against single phase-to-earth faults of high voltage power lines. The aim of invention is to raise the accuracy of distance determination to fault place in single fed and double fed lines. For this purpose, the real and imaginary component of apparent impedance Ýa by classical formula for single phase-to-earth fault are used. As a result, direct sequence reactance X1 to fault place and the fault resistance Rf through which fault current flows are obtained. To enable it, not only specific reactance X1sp of protected line must be used but also several other specific quantities of the line: X0sp - specific zero sequence reactance, Rcsp and R0sp - specific direct sequence and zero sequence resistance of phase conductor, Rgsp - specific ground resistance, for double fed lines Ý0s - zero sequence impedance of the network at the far end of the line, llin - length of the protected line. For single fed lines, the target is achieved by single calculation, for double fed lines, the iterative calculations must be applied. The distance to fault place is calculated using obtained reactance X1 and the specific one X1sp. |
